Amplifier input protection circuits

ABSTRACT

Amplifier input protection circuits are described. In one embodiment, a photoreceiver for a lidar system has a photodetector configured to generate an output current in response to received light. A transimpedance amplifier is configured to receive the output current and generate a voltage output corresponding to the output current in response thereto, and a diode circuit has a cathode coupled at a node between the photodetector output and the transimpedance amplifier input.

TECHNICAL FIELD

This disclosure generally relates to lidar systems and, moreparticularly, to a receiver within the lidar system that includesprotection circuits for an amplifier coupled to a photodiode.

BACKGROUND

Light detection and ranging (lidar) is a technology that can be used tomeasure distances to remote targets. Typically, a lidar system includesa light source and an optical receiver. The light source can include,for example, a laser which emits light having a particular operatingwavelength. The operating wavelength of a lidar system may lie, forexample, in the infrared, visible, or ultraviolet portions of theelectromagnetic spectrum. The light source emits light toward a targetwhich scatters the light, and some of the scattered light is receivedback at the receiver. The system determines the distance to the targetbased on one or more characteristics associated with the received light.For example, the lidar system may determine the distance to the targetbased on the time of flight for a pulse of light emitted by the lightsource to travel to the target and back to the lidar system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example light detection and ranging (lidar)system.

FIG. 2 illustrates an example scan pattern produced by a lidar system.

FIG. 3 illustrates an example lidar system with an example rotatingpolygon mirror.

FIG. 4 illustrates an example light-source field of view (FOV_(L)) andreceiver field of view (FOV_(R)) for a lidar system.

FIG. 5 illustrates an example unidirectional scan pattern that includesmultiple pixels and multiple scan lines.

FIG. 6 illustrates an example InGaAs avalanche photodiode which canoperate in the lidar system of FIG. 1.

FIG. 7 illustrates an example photodiode coupled to a pulse-detectioncircuit, which can operate in the lidar system of FIG. 1.

FIG. 8 illustrates a receiver having a lidar detector disposed directlyon an application specific integrated circuit (ASIC) that processeslight detection signals generated by the receiver.

FIG. 9 illustrates an example lidar detector system that includes aplurality of time to digital convertors (TDCs) to enable enhanced pulseenvelope and range detection;

FIG. 10 illustrates an example plot of detection points that may beproduced by the envelope detector of FIG. 9.

FIG. 11 illustrates a circuit with protection for an amplifier.

FIG. 12 illustrates an alternative circuit with protection for anamplifier.

FIG. 13 illustrates another alternative circuit with protection for anamplifier.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 illustrates an example light detection and ranging (lidar) system100. In particular embodiments, a lidar system 100 may be referred to asa laser ranging system, a laser radar system, a LIDAR system, a lidarsensor, or a laser detection and ranging (LADAR or ladar) system. Inparticular embodiments, a lidar system 100 may include a light source110, mirror 115, scanner 120, receiver 140, or controller 150. The lightsource 110 may include, for example, a laser which emits light having aparticular operating wavelength in the infrared, visible, or ultravioletportions of the electromagnetic spectrum. As an example, light source110 may include a laser with an operating wavelength betweenapproximately 900 nanometers (nm) and 2000 nm. The light source 110emits an output beam of light 125 which may be continuous wave (CW),pulsed, or modulated in any suitable manner for a given application. Theoutput beam of light 125 is directed downrange toward a remote target130. As an example, the remote target 130 may be located a distance D ofapproximately 1 m to 1 km from the lidar system 100.

Once the output beam 125 reaches the downrange target 130, the targetmay scatter or reflect at least a portion of light from the output beam125, and some of the scattered or reflected light may return toward thelidar system 100. In the example of FIG. 1, the scattered or reflectedlight is represented by input beam 135, which passes through scanner 120and is reflected by mirror 115 and directed to receiver 140. Inparticular embodiments, a relatively small fraction of the light fromoutput beam 125 may return to the lidar system 100 as input beam 135. Asan example, the ratio of input beam 135 average power, peak power, orpulse energy to output beam 125 average power, peak power, or pulseenergy may be approximately 10⁻¹, 10⁻², 10⁻³, 10⁻⁴, 10⁻⁵, 10−6, 10⁻⁷,10⁻⁸, 10⁻⁹, 10⁻¹⁰, 10⁻¹¹, or 10⁻¹². As another example, if a pulse ofoutput beam 125 has a pulse energy of 1 microjoule (μJ), then the pulseenergy of a corresponding pulse of input beam 135 may have a pulseenergy of approximately 10 nanojoules (nJ), 1 nJ, 100 picojoules (pJ),10 pJ, 1 pJ, 100 femtojoules (fJ), 10 fJ, 1 fJ, 100 attojoules (aJ), 10aJ, 1 aJ, or 0.1 aJ. In particular embodiments, output beam 125 may bereferred to as an optical signal, laser beam, light beam, optical beam,emitted beam, emitted light, or beam. In particular embodiments, inputbeam 135 may be referred to as a received optical signal, return beam,received beam, return light, received light, input light, scatteredlight, or reflected light. As used herein, scattered light may refer tolight that is scattered or reflected by a target 130. As an example, aninput beam 135 may include: light from the output beam 125 that isscattered by target 130; light from the output beam 125 that isreflected by target 130; or a combination of scattered and reflectedlight from target 130.

In particular embodiments, receiver 140 may receive or detect photonsfrom input beam 135 and produce one or more representative signals. Forexample, the receiver 140 may produce an output electrical signal 145that is representative of the input beam 135, and the electrical signal145 may be sent to controller 150. In particular embodiments, receiver140 or controller 150 may include a processor, computing system (e.g.,an ASIC or FPGA), or other suitable circuitry. A controller 150 may beconfigured to analyze one or more characteristics of the electricalsignal 145 from the receiver 140 to determine one or morecharacteristics of the target 130, such as its distance downrange fromthe lidar system 100. This may be done, for example, by analyzing a timeof flight or a frequency or phase modulation of a transmitted beam oflight 125 or a received beam of light 135. If lidar system 100 measuresa time of flight of T (e.g., T represents a round-trip time of flightfor an emitted pulse of light to travel from the lidar system 100 to thetarget 130 and back to the lidar system 100), then the distance D fromthe target 130 to the lidar system 100 may be expressed as D=c·T/2,where c is the speed of light (approximately 3.0×10⁸ m/s). As anexample, if a time of flight is measured to be T=300 ns, then thedistance from the target 130 to the lidar system 100 may be determinedto be approximately D=45.0 m. As another example, if a time of flight ismeasured to be T=1.33 μs, then the distance from the target 130 to thelidar system 100 may be determined to be approximately D=199.5 m. Inparticular embodiments, a distance D from lidar system 100 to a target130 may be referred to as a distance, depth, or range of target 130. Asused herein, the speed of light c refers to the speed of light in anysuitable medium, such as for example in air, water, or vacuum. As anexample, the speed of light in vacuum is approximately 2.9979×10⁸ m/s,and the speed of light in air (which has a refractive index ofapproximately 1.0003) is approximately 2.9970×10⁸ m/s.

In particular embodiments, light source 110 may include a pulsed or CWlaser. As an example, light source 110 may be a pulsed laser configuredto produce or emit pulses of light with a pulse duration or pulse widthof approximately 10 picoseconds (ps) to 100 nanoseconds (ns). The pulsesmay have a pulse duration of approximately 100 ps, 200 ps, 400 ps, 1 ns,2 ns, 5 ns, 10 ns, 20 ns, 50 ns, 100 ns, or any other suitable pulseduration. As another example, light source 110 may be a pulsed laserthat produces pulses with a pulse duration of approximately 1-5 ns. Asanother example, light source 110 may be a pulsed laser that producespulses at a pulse repetition frequency of approximately 100 kHz to 10MHz or a pulse period (e.g., a time between consecutive pulses) ofapproximately 100 ns to 10 μs. In particular embodiments, light source110 may have a substantially constant pulse repetition frequency, orlight source 110 may have a variable or adjustable pulse repetitionfrequency. As an example, light source 110 may be a pulsed laser thatproduces pulses at a substantially constant pulse repetition frequencyof approximately 640 kHz (e.g., 640,000 pulses per second),corresponding to a pulse period of approximately 1.56 μs. As anotherexample, light source 110 may have a pulse repetition frequency (whichmay be referred to as a repetition rate) that can be varied fromapproximately 200 kHz to 3 MHz. As used herein, a pulse of light may bereferred to as an optical pulse, a light pulse, or a pulse.

In particular embodiments, light source 110 may include a pulsed or CWlaser that produces a free-space output beam 125 having any suitableaverage optical power. As an example, output beam 125 may have anaverage power of approximately 1 milliwatt (mW), 10 mW, 100 mW, 1 watt(W), 10 W, or any other suitable average power. In particularembodiments, output beam 125 may include optical pulses with anysuitable pulse energy or peak optical power. As an example, output beam125 may include pulses with a pulse energy of approximately 0.01 μJ, 0.1μJ, 0.5 μJ, 1 μJ, 2 μJ, 10 μJ, 100 μJ, 1 mJ, or any other suitable pulseenergy. As another example, output beam 125 may include pulses with apeak power of approximately 10 W, 100 W, 1 kW, 5 kW, 10 kW, or any othersuitable peak power. The peak power (P_(peak)) of a pulse of light canbe related to the pulse energy (E) by the expression E=P_(peak)·Δt,where Δt is the duration of the pulse, and the duration of a pulse maybe defined as the full width at half maximum duration of the pulse. Forexample, an optical pulse with a duration of 1 ns and a pulse energy of1 μJ has a peak power of approximately 1 kW. The average power (P_(av))of an output beam 125 can be related to the pulse repetition frequency(PRF) and pulse energy by the expression P_(av)=PRF·E. For example, ifthe pulse repetition frequency is 500 kHz, then the average power of anoutput beam 125 with 1-μJ pulses is approximately 0.5 W.

In particular embodiments, light source 110 may include a laser diode,such as for example, a Fabry-Perot laser diode, a quantum well laser, adistributed Bragg reflector (DBR) laser, a distributed feedback (DFB)laser, a vertical-cavity surface-emitting laser (VCSEL), a quantum dotlaser diode, a grating-coupled surface-emitting laser (GCSEL), aslab-coupled optical waveguide laser (SCOWL), a single-transverse-modelaser diode, a multi-mode broad area laser diode, a laser-diode bar, alaser-diode stack, or a tapered-stripe laser diode. As an example, lightsource 110 may include an aluminum-gallium-arsenide (AlGaAs) laserdiode, an indium-gallium-arsenide (InGaAs) laser diode, anindium-gallium-arsenide-phosphide (InGaAsP) laser diode, or a laserdiode that includes any suitable combination of aluminum (Al), indium(In), gallium (Ga), arsenic (As), phosphorous (P), or any other suitablematerial. In particular embodiments, light source 110 may include apulsed or CW laser diode with a peak emission wavelength between 1200 nmand 1600 nm. As an example, light source 110 may include acurrent-modulated InGaAsP DFB laser diode that produces optical pulsesat a wavelength of approximately 1550 nm.

In particular embodiments, light source 110 may include a pulsed or CWlaser diode followed by one or more optical-amplification stages. Apulsed laser diode may produce relatively low-power optical seed pulseswhich are amplified by an optical amplifier. As an example, light source110 may be a fiber-laser module that includes a current-modulated laserdiode with an operating wavelength of approximately 1550 nm followed bya single-stage or a multi-stage erbium-doped fiber amplifier (EDFA) orerbium-ytterbium-doped fiber amplifier (EYDFA) that amplifies the seedpulses from the laser diode. As another example, light source 110 mayinclude a continuous-wave (CW) or quasi-CW laser diode followed by anexternal optical modulator (e.g., an electro-optic amplitude modulator).The optical modulator may modulate the CW light from the laser diode toproduce optical pulses which are sent to an optical amplifier. Asanother example, light source 110 may include a pulsed or CW laser diodefollowed by a semiconductor optical amplifier (SOA). The SOA may includean active optical waveguide configured to receive light from the laserdiode and amplify the light as it propagates through the waveguide. TheSOA may be integrated on the same chip as the laser diode, or the SOAmay be a separate device with an anti-reflection coating on its inputfacet or output facet.

In particular embodiments, light source 110 may include a direct-emitterlaser diode. A direct-emitter laser diode (which may be referred to as adirect emitter) may include a laser diode which produces light that isnot subsequently amplified by an optical amplifier. A light source 110that includes a direct-emitter laser diode may not include an opticalamplifier, and the output light produced by a direct emitter may not beamplified after it is emitted by the laser diode. The light produced bya direct-emitter laser diode (e.g., optical pulses, CW light, orfrequency-modulated light) may be emitted directly as a free-spaceoutput beam 125 without being amplified. A direct-emitter laser diodemay be driven by an electrical power source that supplies current pulsesto the laser diode, and each current pulse may result in the emission ofan output optical pulse.

In particular embodiments, light source 110 may include a diode-pumpedsolid-state (DPSS) laser. A DPSS laser (which may be referred to as asolid-state laser) may refer to a laser that includes a solid-state,glass, ceramic, or crystal-based gain medium that is pumped by one ormore pump laser diodes. The gain medium may include a host material thatis doped with rare-earth ions (e.g., neodymium, erbium, ytterbium, orpraseodymium). For example, a gain medium may include a yttrium aluminumgarnet (YAG) crystal that is doped with neodymium (Nd) ions, and thegain medium may be referred to as a Nd:YAG crystal. A DPSS laser with aNd:YAG gain medium may produce light at a wavelength betweenapproximately 1300 nm and approximately 1400 nm, and the Nd:YAG gainmedium may be pumped by one or more pump laser diodes with an operatingwavelength between approximately 730 nm and approximately 900 nm. A DPSSlaser may be a passively Q-switched laser that includes a saturableabsorber (e.g., a vanadium-doped crystal that acts as a saturableabsorber). Alternatively, a DPSS laser may be an actively Q-switchedlaser that includes an active Q-switch (e.g., an acousto-optic modulatoror an electro-optic modulator). A passively or actively Q-switched DPSSlaser may produce output optical pulses that form an output beam 125 ofa lidar system 100.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be a collimated optical beam having any suitable beamdivergence, such as for example, a full-angle beam divergence ofapproximately 0.5 to 10 milliradians (mrad). A divergence of output beam125 may refer to an angular measure of an increase in beam size (e.g., abeam radius or beam diameter) as output beam 125 travels away from lightsource 110 or lidar system 100. In particular embodiments, output beam125 may have a substantially circular cross section with a beamdivergence characterized by a single divergence value. As an example, anoutput beam 125 with a circular cross section and a full-angle beamdivergence of 2 mrad may have a beam diameter or spot size ofapproximately 20 cm at a distance of 100 m from lidar system 100. Inparticular embodiments, output beam 125 may have a substantiallyelliptical cross section characterized by two divergence values. As anexample, output beam 125 may have a fast axis and a slow axis, where thefast-axis divergence is greater than the slow-axis divergence. Asanother example, output beam 125 may be an elliptical beam with afast-axis divergence of 4 mrad and a slow-axis divergence of 2 mrad.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be unpolarized or randomly polarized, may have nospecific or fixed polarization (e.g., the polarization may vary withtime), or may have a particular polarization (e.g., output beam 125 maybe linearly polarized, elliptically polarized, or circularly polarized).As an example, light source 110 may produce light with no specificpolarization or may produce light that is linearly polarized.

In particular embodiments, lidar system 100 may include one or moreoptical components configured to reflect, focus, filter, shape, modify,steer, or direct light within the lidar system 100 or light produced orreceived by the lidar system 100 (e.g., output beam 125 or input beam135). As an example, lidar system 100 may include one or more lenses,mirrors, filters (e.g., bandpass or interference filters), beamsplitters, polarizers, polarizing beam splitters, wave plates (e.g.,half-wave or quarter-wave plates), diffractive elements, holographicelements, isolators, couplers, detectors, beam combiners, orcollimators. The optical components in a lidar system 100 may befree-space optical components, fiber-coupled optical components, or acombination of free-space and fiber-coupled optical components.

In particular embodiments, lidar system 100 may include a telescope, oneor more lenses, or one or more mirrors configured to expand, focus, orcollimate the output beam 125 or the input beam 135 to a desired beamdiameter or divergence. As an example, the lidar system 100 may includeone or more lenses to focus the input beam 135 onto a photodetector ofreceiver 140. As another example, the lidar system 100 may include oneor more flat mirrors or curved mirrors (e.g., concave, convex, orparabolic mirrors) to steer or focus the output beam 125 or the inputbeam 135. For example, the lidar system 100 may include an off-axisparabolic mirror to focus the input beam 135 onto a photodetector ofreceiver 140. As illustrated in FIG. 1, the lidar system 100 may includemirror 115 (which may be a metallic or dielectric mirror), and mirror115 may be configured so that light beam 125 passes through the mirror115 or passes along an edge or side of the mirror 115 and input beam 135is reflected toward the receiver 140. As an example, mirror 115 (whichmay be referred to as an overlap mirror, superposition mirror, orbeam-combiner mirror) may include a hole, slot, or aperture which outputlight beam 125 passes through. As another example, rather than passingthrough the mirror 115, the output beam 125 may be directed to passalongside the mirror 115 with a gap (e.g., a gap of width approximately0.1 mm, 0.5 mm, 1 mm, 2 mm, 5 mm, or 10 mm) between the output beam 125and an edge of the mirror 115.

In particular embodiments, mirror 115 may provide for output beam 125and input beam 135 to be substantially coaxial so that the two beamstravel along approximately the same optical path (albeit in oppositedirections). The input and output beams being substantially coaxial mayrefer to the beams being at least partially overlapped or sharing acommon propagation axis so that input beam 135 and output beam 125travel along substantially the same optical path (albeit in oppositedirections). As an example, output beam 125 and input beam 135 may beparallel to each other to within less than 10 mrad, 5 mrad, 2 mrad, 1mrad, 0.5 mrad, or 0.1 mrad. As output beam 125 is scanned across afield of regard, the input beam 135 may follow along with the outputbeam 125 so that the coaxial relationship between the two beams ismaintained.

In particular embodiments, lidar system 100 may include a scanner 120configured to scan an output beam 125 across a field of regard of thelidar system 100. As an example, scanner 120 may include one or morescanning mirrors configured to pivot, rotate, oscillate, or move in anangular manner about one or more rotation axes. The output beam 125 maybe reflected by a scanning mirror, and as the scanning mirror pivots orrotates, the reflected output beam 125 may be scanned in a correspondingangular manner. As an example, a scanning mirror may be configured toperiodically pivot back and forth over a 30-degree range, which resultsin the output beam 125 scanning back and forth across a 60-degree range(e.g., a 0-degree rotation by a scanning mirror results in a 20-degreeangular scan of output beam 125).

In particular embodiments, a scanning mirror may be attached to ormechanically driven by a scanner actuator or mechanism which pivots orrotates the mirror over a particular angular range (e.g., over a 5°angular range, 30° angular range, 60° angular range, 120° angular range,360° angular range, or any other suitable angular range). A scanneractuator or mechanism configured to pivot or rotate a mirror may includea galvanometer scanner, a resonant scanner, a piezoelectric actuator, avoice coil motor, an electric motor (e.g., a DC motor, a brushless DCmotor, a synchronous electric motor, or a stepper motor), amicroelectromechanical systems (MEMS) device, or any other suitableactuator or mechanism. As an example, a scanner 120 may include ascanning mirror attached to a galvanometer scanner configured to pivotback and forth over a 30° angular range. As another example, a scanner120 may include a polygon mirror configured to rotate continuously inthe same direction (e.g., rather than pivoting back and forth, thepolygon mirror continuously rotates 360 degrees in a clockwise orcounterclockwise direction). The polygon mirror may be coupled orattached to a synchronous motor configured to rotate the polygon mirrorat a substantially fixed rotational frequency (e.g., a rotationalfrequency of approximately 1 Hz, 10 Hz, 50 Hz, 100 Hz, 500 Hz, or 1,000Hz).

In particular embodiments, scanner 120 may be configured to scan theoutput beam 125 (which may include at least a portion of the lightemitted by light source 110) across a field of regard of the lidarsystem 100. A field of regard (FOR) of a lidar system 100 may refer toan area, region, or angular range over which the lidar system 100 may beconfigured to scan or capture distance information. As an example, alidar system 100 with an output beam 125 with a 30-degree scanning rangemay be referred to as having a 30-degree angular field of regard. Asanother example, a lidar system 100 with a scanning mirror that rotatesover a 30-degree range may produce an output beam 125 that scans acrossa 60-degree range (e.g., a 60-degree FOR). In particular embodiments,lidar system 100 may have a FOR of approximately 10°, 20°, 40°, 60°,120°, 360°, or any other suitable FOR.

In particular embodiments, scanner 120 may be configured to scan theoutput beam 125 horizontally and vertically, and lidar system 100 mayhave a particular FOR along the horizontal direction and anotherparticular FOR along the vertical direction. As an example, lidar system100 may have a horizontal FOR of 10° to 120° and a vertical FOR of 2° to45°. In particular embodiments, scanner 120 may include a first scanmirror and a second scan mirror, where the first scan mirror directs theoutput beam 125 toward the second scan mirror, and the second scanmirror directs the output beam 125 downrange from the lidar system 100.As an example, the first scan mirror may scan the output beam 125 alonga first direction, and the second scan mirror may scan the output beam125 along a second direction that is substantially orthogonal to thefirst direction. As another example, the first scan mirror may scan theoutput beam 125 along a substantially horizontal direction, and thesecond scan mirror may scan the output beam 125 along a substantiallyvertical direction (or vice versa). As another example, the first andsecond scan mirrors may each be driven by galvanometer scanners. Asanother example, the first or second scan mirror may include a polygonmirror driven by an electric motor. In particular embodiments, scanner120 may be referred to as a beam scanner, optical scanner, or laserscanner.

In particular embodiments, one or more scanning mirrors may becommunicatively coupled to controller 150 which may control the scanningmirror(s) so as to guide the output beam 125 in a desired directiondownrange or along a desired scan pattern. In particular embodiments, ascan pattern may refer to a pattern or path along which the output beam125 is directed. As an example, scanner 120 may include two scanningmirrors configured to scan the output beam 125 across a 60° horizontalFOR and a 20° vertical FOR. The two scanner mirrors may be controlled tofollow a scan path that substantially covers the 60°×20° FOR. As anexample, the scan path may result in a point cloud with pixels thatsubstantially cover the 60°×20° FOR. The pixels may be approximatelyevenly distributed across the 60°×20° FOR. Alternatively, the pixels mayhave a particular nonuniform distribution (e.g., the pixels may bedistributed across all or a portion of the 60°×20° FOR, and the pixelsmay have a higher density in one or more particular regions of the60°×20° FOR).

In particular embodiments, a lidar system 100 may include a light source110 configured to emit pulses of light and a scanner 120 configured toscan at least a portion of the emitted pulses of light across a field ofregard of the lidar system 100. One or more of the emitted pulses oflight may be scattered by a target 130 located downrange from the lidarsystem 100, and a receiver 140 may detect at least a portion of thepulses of light scattered by the target 130. A receiver 140 may bereferred to as a photoreceiver, optical receiver, optical sensor,detector, photodetector, or optical detector. In particular embodiments,lidar system 100 may include a receiver 140 that receives or detects atleast a portion of input beam 135 and produces an electrical signal thatcorresponds to input beam 135. As an example, if input beam 135 includesan optical pulse, then receiver 140 may produce an electrical current orvoltage pulse that corresponds to the optical pulse detected by receiver140. As another example, receiver 140 may include one or more avalanchephotodiodes (APDs) or one or more single-photon avalanche diodes(SPADs). As another example, receiver 140 may include one or more PNphotodiodes (e.g., a photodiode structure formed by a p-typesemiconductor and a n-type semiconductor, where the PN acronym refers tothe structure having p-doped and n-doped regions) or one or more PINphotodiodes (e.g., a photodiode structure formed by an undoped intrinsicsemiconductor region located between p-type and n-type regions, wherethe PIN acronym refers to the structure having p-doped, intrinsic, andn-doped regions). An APD, SPAD, PN photodiode, or PIN photodiode mayeach be referred to as a detector, photodetector, or photodiode. Adetector may have an active region or an avalanche-multiplication regionthat includes silicon, germanium, InGaAs, or AlInAsSb (aluminum indiumarsenide antimonide). The active region may refer to an area over whicha detector may receive or detect input light. An active region may haveany suitable size or diameter, such as for example, a diameter ofapproximately 10 μm, 25 μm, 50 μm, 80 μm, 100 μm, 200 μm, 500 μm, 1 mm,2 mm, or 5 mm.

In particular embodiments, receiver 140 may include electronic circuitrythat performs signal amplification, sampling, filtering, signalconditioning, analog-to-digital conversion, time-to-digital conversion,pulse detection, threshold detection, rising-edge detection, orfalling-edge detection. As an example, receiver 140 may include atransimpedance amplifier that converts a received photocurrent (e.g., acurrent produced by an APD in response to a received optical signal)into a voltage signal. The voltage signal may be sent to pulse-detectioncircuitry that produces an analog or digital output signal 145 thatcorresponds to one or more optical characteristics (e.g., rising edge,falling edge, amplitude, duration, or energy) of a received opticalpulse. As an example, the pulse-detection circuitry may perform atime-to-digital conversion to produce a digital output signal 145. Theelectrical output signal 145 may be sent to controller 150 forprocessing or analysis (e.g., to determine a time-of-flight valuecorresponding to a received optical pulse).

In particular embodiments, controller 150 may be electrically coupled orcommunicatively coupled to light source 110, scanner 120, or receiver140. As an example, controller 150 may receive electrical trigger pulsesor edges from light source 110, where each pulse or edge corresponds tothe emission of an optical pulse by light source 110. As anotherexample, controller 150 may provide instructions, a control signal, or atrigger signal to light source 110 indicating when light source 110should produce optical pulses. Controller 150 may send an electricaltrigger signal that includes electrical pulses, where each electricalpulse results in the emission of an optical pulse by light source 110.In particular embodiments, the frequency, period, duration, pulseenergy, peak power, average power, or wavelength of the optical pulsesproduced by light source 110 may be adjusted based on instructions, acontrol signal, or trigger pulses provided by controller 150. Inparticular embodiments, controller 150 may be coupled to light source110 and receiver 140, and controller 150 may determine a time-of-flightvalue for an optical pulse based on timing information associated withwhen the pulse was emitted by light source 110 and when a portion of thepulse (e.g., input beam 135) was detected or received by receiver 140.In particular embodiments, controller 150 may include circuitry thatperforms signal amplification, sampling, filtering, signal conditioning,analog-to-digital conversion, time-to-digital conversion, pulsedetection, threshold detection, rising-edge detection, or falling-edgedetection.

In particular embodiments, lidar system 100 may include one or moreprocessors (e.g., a controller 150) configured to determine a distance Dfrom the lidar system 100 to a target 130 based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system 100 to the target 130 and back to the lidar system 100.The target 130 may be at least partially contained within a field ofregard of the lidar system 100 and located a distance D from the lidarsystem 100 that is less than or equal to an operating range (R_(OP)) ofthe lidar system 100. In particular embodiments, an operating range(which may be referred to as an operating distance) of a lidar system100 may refer to a distance over which the lidar system 100 isconfigured to sense or identify targets 130 located within a field ofregard of the lidar system 100. The operating range of lidar system 100may be any suitable distance, such as for example, 25 m, 50 m, 100 m,200 m, 500 m, or 1 km. As an example, a lidar system 100 with a 200-moperating range may be configured to sense or identify various targets130 located up to 200 m away from the lidar system 100. The operatingrange R_(OP) of a lidar system 100 may be related to the time τ betweenthe emission of successive optical signals by the expressionR_(OP)=c·τ/2. For a lidar system 100 with a 200-m operating range(R_(OP)=200 m), the time τ between successive pulses (which may bereferred to as the pulse period) is approximately 2·R_(OP)/c≅1.33 μs.The pulse period T may also correspond to the time of flight for a pulseto travel to and from a target 130 located a distance R_(OP) from thelidar system 100. Additionally, the pulse period τ may be related to thepulse repetition frequency (PRF) by the expression τ=1/PRF. For example,a pulse period of 1.33 μs corresponds to a PRF of approximately 752 kHz.

In particular embodiments, a lidar system 100 may be used to determinethe distance to one or more downrange targets 130. By scanning the lidarsystem 100 across a field of regard, the system may be used to map thedistance to a number of points within the field of regard. Each of thesedepth-mapped points may be referred to as a pixel or a voxel. Acollection of pixels captured in succession (which may be referred to asa depth map, a point cloud, or a frame) may be rendered as an image ormay be analyzed to identify or detect objects or to determine a shape ordistance of objects within the FOR. As an example, a point cloud maycover a field of regard that extends 60° horizontally and 15°vertically, and the point cloud may include a frame of 100-2000 pixelsin the horizontal direction by 4-400 pixels in the vertical direction.

In particular embodiments, lidar system 100 may be configured torepeatedly capture or generate point clouds of a field of regard at anysuitable frame rate between approximately 0.1 frames per second (FPS)and approximately 1,000 FPS. As an example, lidar system 100 maygenerate point clouds at a frame rate of approximately 0.1 FPS, 0.5 FPS,1 FPS, 2 FPS, 5 FPS, 10 FPS, 20 FPS, 100 FPS, 500 FPS, or 1,000 FPS. Asanother example, lidar system 100 may be configured to produce opticalpulses at a rate of 5×10⁵ pulses/second (e.g., the system may determine500,000 pixel distances per second) and scan a frame of 1000×50 pixels(e.g., 50,000 pixels/frame), which corresponds to a point-cloud framerate of 10 frames per second (e.g., 10 point clouds per second). Inparticular embodiments, a point-cloud frame rate may be substantiallyfixed, or a point-cloud frame rate may be dynamically adjustable. As anexample, a lidar system 100 may capture one or more point clouds at aparticular frame rate (e.g., 1 Hz) and then switch to capture one ormore point clouds at a different frame rate (e.g., 10 Hz). A slowerframe rate (e.g., 1 Hz) may be used to capture one or morehigh-resolution point clouds, and a faster frame rate (e.g., 10 Hz) maybe used to rapidly capture multiple lower-resolution point clouds.

In particular embodiments, a lidar system 100 may be configured tosense, identify, or determine distances to one or more targets 130within a field of regard. As an example, a lidar system 100 maydetermine a distance to a target 130, where all or part of the target130 is contained within a field of regard of the lidar system 100. Allor part of a target 130 being contained within a FOR of the lidar system100 may refer to the FOR overlapping, encompassing, or enclosing atleast a portion of the target 130. In particular embodiments, target 130may include all or part of an object that is moving or stationaryrelative to lidar system 100. As an example, target 130 may include allor a portion of a person, vehicle, motorcycle, truck, train, bicycle,wheelchair, pedestrian, animal, road sign, traffic light, lane marking,road-surface marking, parking space, pylon, guard rail, traffic barrier,pothole, railroad crossing, obstacle in or near a road, curb, stoppedvehicle on or beside a road, utility pole, house, building, trash can,mailbox, tree, any other suitable object, or any suitable combination ofall or part of two or more objects. In particular embodiments, a targetmay be referred to as an object.

In particular embodiments, light source 110, scanner 120, and receiver140 may be packaged together within a single housing, where a housingmay refer to a box, case, or enclosure that holds or contains all orpart of a lidar system 100. As an example, a lidar-system enclosure maycontain a light source 110, mirror 115, scanner 120, and receiver 140 ofa lidar system 100. Additionally, the lidar-system enclosure may includea controller 150. The lidar-system enclosure may also include one ormore electrical connections for conveying electrical power or electricalsignals to or from the enclosure. In particular embodiments, one or morecomponents of a lidar system 100 may be located remotely from alidar-system enclosure. As an example, all or part of light source 110may be located remotely from a lidar-system enclosure, and pulses oflight produced by the light source 110 may be conveyed to the enclosurevia optical fiber. As another example, all or part of a controller 150may be located remotely from a lidar-system enclosure.

In particular embodiments, light source 110 may include an eye-safelaser, or lidar system 100 may be classified as an eye-safe laser systemor laser product. An eye-safe laser, laser system, or laser product mayrefer to a system that includes a laser with an emission wavelength,average power, peak power, peak intensity, pulse energy, beam size, beamdivergence, exposure time, or scanned output beam such that emittedlight from the system presents little or no possibility of causingdamage to a person's eyes. As an example, light source 110 or lidarsystem 100 may be classified as a Class 1 laser product (as specified bythe 60825-1 standard of the International Electrotechnical Commission(IEC)) or a Class I laser product (as specified by Title 21, Section1040.10 of the United States Code of Federal Regulations (CFR)) that issafe under all conditions of normal use. In particular embodiments,lidar system 100 may be an eye-safe laser product (e.g., with a Class 1or Class I classification) configured to operate at any suitablewavelength between approximately 900 nm and approximately 2100 nm. As anexample, lidar system 100 may include a laser with an operatingwavelength between approximately 1200 nm and approximately 1400 nm orbetween approximately 1400 nm and approximately 1600 nm, and the laseror the lidar system 100 may be operated in an eye-safe manner. Asanother example, lidar system 100 may be an eye-safe laser product thatincludes a scanned laser with an operating wavelength betweenapproximately 1530 nm and approximately 1560 nm. As another example,lidar system 100 may be a Class 1 or Class I laser product that includesa laser diode, fiber laser, or solid-state laser with an operatingwavelength between approximately 1200 nm and approximately 1600 nm.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle. As an example, multiple lidar systems 100 maybe integrated into a car to provide a complete 360-degree horizontal FORaround the car. As another example, 4-10 lidar systems 100, each systemhaving a 45-degree to 90-degree horizontal FOR, may be combined togetherto form a sensing system that provides a point cloud covering a360-degree horizontal FOR. The lidar systems 100 may be oriented so thatadjacent FORs have an amount of spatial or angular overlap to allow datafrom the multiple lidar systems 100 to be combined or stitched togetherto form a single or continuous 360-degree point cloud. As an example,the FOR of each lidar system 100 may have approximately 1-15 degrees ofoverlap with an adjacent FOR. In particular embodiments, a vehicle mayrefer to a mobile machine configured to transport people or cargo. Forexample, a vehicle may include, may take the form of, or may be referredto as a car, automobile, motor vehicle, truck, bus, van, trailer,off-road vehicle, farm vehicle, lawn mower, construction equipment,forklift, robot, golf cart, motorhome, taxi, motorcycle, scooter,bicycle, skateboard, train, snowmobile, watercraft (e.g., a ship orboat), aircraft (e.g., a fixed-wing aircraft, helicopter, or dirigible),unmanned aerial vehicle (e.g., drone), or spacecraft. In particularembodiments, a vehicle may include an internal combustion engine or anelectric motor that provides propulsion for the vehicle.

In particular embodiments, one or more lidar systems 100 may be includedin a vehicle as part of an advanced driver assistance system (ADAS) toassist a driver of the vehicle in operating the vehicle. For example, alidar system 100 may be part of an ADAS that provides information orfeedback to a driver (e.g., to alert the driver to potential problems orhazards) or that automatically takes control of part of a vehicle (e.g.,a braking system or a steering system) to avoid collisions or accidents.A lidar system 100 may be part of a vehicle ADAS that provides adaptivecruise control, automated braking, automated parking, collisionavoidance, alerts the driver to hazards or other vehicles, maintains thevehicle in the correct lane, or provides a warning if an object oranother vehicle is in a blind spot.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle as part of an autonomous-vehicle drivingsystem. As an example, a lidar system 100 may provide information aboutthe surrounding environment to a driving system of an autonomousvehicle. An autonomous-vehicle driving system may be configured to guidethe autonomous vehicle through an environment surrounding the vehicleand toward a destination. An autonomous-vehicle driving system mayinclude one or more computing systems that receive information from alidar system 100 about the surrounding environment, analyze the receivedinformation, and provide control signals to the vehicle's drivingsystems (e.g., steering wheel, accelerator, brake, or turn signal). Asan example, a lidar system 100 integrated into an autonomous vehicle mayprovide an autonomous-vehicle driving system with a point cloud every0.1 seconds (e.g., the point cloud has a 10 Hz update rate, representing10 frames per second). The autonomous-vehicle driving system may analyzethe received point clouds to sense or identify targets 130 and theirrespective locations, distances, or speeds, and the autonomous-vehicledriving system may update control signals based on this information. Asan example, if lidar system 100 detects a vehicle ahead that is slowingdown or stopping, the autonomous-vehicle driving system may sendinstructions to release the accelerator and apply the brakes.

In particular embodiments, an autonomous vehicle may be referred to asan autonomous car, driverless car, self-driving car, robotic car, orunmanned vehicle. In particular embodiments, an autonomous vehicle mayrefer to a vehicle configured to sense its environment and navigate ordrive with little or no human input. As an example, an autonomousvehicle may be configured to drive to any suitable location and controlor perform all safety-critical functions (e.g., driving, steering,braking, parking) for the entire trip, with the driver not expected tocontrol the vehicle at any time. As another example, an autonomousvehicle may allow a driver to safely turn their attention away fromdriving tasks in particular environments (e.g., on freeways), or anautonomous vehicle may provide control of a vehicle in all but a fewenvironments, requiring little or no input or attention from the driver.

In particular embodiments, an autonomous vehicle may be configured todrive with a driver present in the vehicle, or an autonomous vehicle maybe configured to operate the vehicle with no driver present. As anexample, an autonomous vehicle may include a driver's seat withassociated controls (e.g., steering wheel, accelerator pedal, and brakepedal), and the vehicle may be configured to drive with no one seated inthe driver's seat or with little or no input from a person seated in thedriver's seat. As another example, an autonomous vehicle may not includeany driver's seat or associated driver's controls, and the vehicle mayperform substantially all driving functions (e.g., driving, steering,braking, parking, and navigating) without human input. As anotherexample, an autonomous vehicle may be configured to operate without adriver (e.g., the vehicle may be configured to transport humanpassengers or cargo without a driver present in the vehicle). As anotherexample, an autonomous vehicle may be configured to operate without anyhuman passengers (e.g., the vehicle may be configured for transportationof cargo without having any human passengers onboard the vehicle).

In particular embodiments, an optical signal (which may be referred toas a light signal, a light waveform, an optical waveform, an outputbeam, or emitted light) may include pulses of light, CW light,amplitude-modulated light, frequency-modulated light, or any suitablecombination thereof. Although this disclosure describes or illustratesexample embodiments of lidar systems 100 or light sources 110 thatproduce optical signals that include pulses of light, the embodimentsdescribed or illustrated herein may also be applied, where appropriate,to other types of optical signals, including continuous-wave (CW) light,amplitude-modulated optical signals, or frequency-modulated opticalsignals. For example, a lidar system 100 as described or illustratedherein may include a light source 110 configured to produce pulses oflight. Alternatively, a lidar system 100 may be configured to operate asa frequency-modulated continuous-wave (FMCW) lidar system and mayinclude a light source 110 configured to produce CW light or afrequency-modulated optical signal.

In particular embodiments, a lidar system 100 may be a FMCW lidar systemwhere the emitted light from the light source 110 (e.g., output beam 125in FIG. 1 or FIG. 3) includes frequency-modulated light. A pulsed lidarsystem is a type of lidar system 100 in which the light source 110 emitspulses of light, and the distance to a remote target 130 is determinedfrom the time-of-flight for a pulse of light to travel to the target 130and back. Another type of lidar system 100 is a frequency-modulatedlidar system, which may be referred to as a frequency-modulatedcontinuous-wave (FMCW) lidar system. A FMCW lidar system usesfrequency-modulated light to determine the distance to a remote target130 based on a modulation frequency of the received light (which isscattered by the remote target) relative to the modulation frequency ofthe emitted light. A round-trip time for the emitted light to travel toa target 130 and back to the lidar system may correspond to a frequencydifference between the received scattered light and a portion of theemitted light.

For example, for a linearly chirped light source (e.g., a frequencymodulation that produces a linear change in frequency with time), thelarger the frequency difference between the emitted light and thereceived light, the farther away the target 130 is located. Thefrequency difference may be determined by mixing the received light witha portion of the emitted light (e.g., by coupling the two beams onto adetector, or by mixing analog electric signals corresponding to thereceived light and the emitted light) and determining the resulting beatfrequency. For example, an electrical signal from an APD may be analyzedusing a fast Fourier transform (FFT) technique to determine thefrequency difference between the emitted light and the received light.If a linear frequency modulation m (e.g., in units of Hz/s) is appliedto a CW laser, then the round-trip time T may be related to thefrequency difference between the received scattered light and theemitted light Δf by the expression T=Δf/m. Additionally, the distance Dfrom the target 130 to the lidar system 100 may be expressed asD=c·Δf/(2 m), where c is the speed of light. For example, for a lightsource 110 with a linear frequency modulation of 10¹² Hz/s (or, 1MHz/μs), if a frequency difference (between the received scattered lightand the emitted light) of 330 kHz is measured, then the distance to thetarget is approximately 50 meters (which corresponds to a round-triptime of approximately 330 ns). As another example, a frequencydifference of 1.33 MHz corresponds to a target located approximately 200meters away.

The light source 110 for a FMCW lidar system may be a fiber laser (e.g.,a seed laser diode followed by one or more optical amplifiers) or adirect-emitter laser diode. The seed laser diode or the direct-emitterlaser diode may be operated in a CW manner (e.g., by driving the laserdiode with a substantially constant DC current), and the frequencymodulation may be provided by an external modulator (e.g., anelectro-optic phase modulator). Alternatively, the frequency modulationmay be produced by applying a DC bias current along with a currentmodulation to the seed laser diode or the direct-emitter laser diode.The current modulation produces a corresponding refractive-indexmodulation in the laser diode, which results in a frequency modulationof the light emitted by the laser diode. The current-modulationcomponent (and corresponding frequency modulation) may have any suitablefrequency or shape (e.g., piecewise linear, sinusoidal, triangle-wave,or sawtooth).

FIG. 2 illustrates an example scan pattern 200 produced by a lidarsystem 100. A scan pattern 200 (which may be referred to as an opticalscan pattern, optical scan path, scan path, or scan) may represent apath or course followed by output beam 125 as it is scanned across allor part of a FOR. Each traversal of a scan pattern 200 may correspond tothe capture of a single frame or a single point cloud. In particularembodiments, a lidar system 100 may be configured to scan output opticalbeam 125 along one or more particular scan patterns 200. In particularembodiments, a scan pattern 200 may scan across any suitable field ofregard (FOR) having any suitable horizontal FOR (FOR_(H)) and anysuitable vertical FOR (FOR_(V)). For example, a scan pattern 200 mayhave a field of regard represented by angular dimensions (e.g.,FOR_(H)×FOR_(V)) 40°×30°, 90°×40°, or 60°×15°. As another example, ascan pattern 200 may have a FOR_(H) greater than or equal to 10°, 25°,30°, 40°, 60°, 90°, or 120°. As another example, a scan pattern 200 mayhave a FOR_(V) greater than or equal to 2°, 5°, 10°, 15°, 20°, 30°, or45°.

In the example of FIG. 2, reference line 220 represents a center of thefield of regard of scan pattern 200. In particular embodiments,reference line 220 may have any suitable orientation, such as forexample, a horizontal angle of 0° (e.g., reference line 220 may beoriented straight ahead) and a vertical angle of 0° (e.g., referenceline 220 may have an inclination of 0°), or reference line 220 may havea nonzero horizontal angle or a nonzero inclination (e.g., a verticalangle of +10° or −10°. In FIG. 2, if the scan pattern 200 has a 60°×15°field of regard, then scan pattern 200 covers a ±30° horizontal rangewith respect to reference line 220 and a ±7.5° vertical range withrespect to reference line 220. Additionally, optical beam 125 in FIG. 2has an orientation of approximately −15° horizontal and +3° verticalwith respect to reference line 220. Optical beam 125 may be referred toas having an azimuth of −15° and an altitude of +3° relative toreference line 220. In particular embodiments, an azimuth (which may bereferred to as an azimuth angle) may represent a horizontal angle withrespect to reference line 220, and an altitude (which may be referred toas an altitude angle, elevation, or elevation angle) may represent avertical angle with respect to reference line 220.

In particular embodiments, a scan pattern 200 may include multiplepixels 210, and each pixel 210 may be associated with one or more laserpulses or one or more distance measurements. Additionally, a scanpattern 200 may include multiple scan lines 230, where each scan linerepresents one scan across at least part of a field of regard, and eachscan line 230 may include multiple pixels 210. In FIG. 2, scan line 230includes five pixels 210 and corresponds to an approximately horizontalscan across the FOR from right to left, as viewed from the lidar system100. In particular embodiments, a cycle of scan pattern 200 may includea total of P_(x)×P_(y) pixels 210 (e.g., a two-dimensional distributionof P_(x) by P_(y) pixels). As an example, scan pattern 200 may include adistribution with dimensions of approximately 100-2,000 pixels 210 alonga horizontal direction and approximately 4-400 pixels 210 along avertical direction. As another example, scan pattern 200 may include adistribution of 1,000 pixels 210 along the horizontal direction by 64pixels 210 along the vertical direction (e.g., the frame size is 1000×64pixels) for a total of 64,000 pixels per cycle of scan pattern 200. Inparticular embodiments, the number of pixels 210 along a horizontaldirection may be referred to as a horizontal resolution of scan pattern200, and the number of pixels 210 along a vertical direction may bereferred to as a vertical resolution. As an example, scan pattern 200may have a horizontal resolution of greater than or equal to 100 pixels210 and a vertical resolution of greater than or equal to 4 pixels 210.As another example, scan pattern 200 may have a horizontal resolution of100-2,000 pixels 210 and a vertical resolution of 4-400 pixels 210.

In particular embodiments, each pixel 210 may be associated with adistance (e.g., a distance to a portion of a target 130 from which anassociated laser pulse was scattered) or one or more angular values. Asan example, a pixel 210 may be associated with a distance value and twoangular values (e.g., an azimuth and altitude) that represent theangular location of the pixel 210 with respect to the lidar system 100.A distance to a portion of target 130 may be determined based at leastin part on a time-of-flight measurement for a corresponding pulse. Anangular value (e.g., an azimuth or altitude) may correspond to an angle(e.g., relative to reference line 220) of output beam 125 (e.g., when acorresponding pulse is emitted from lidar system 100) or an angle ofinput beam 135 (e.g., when an input signal is received by lidar system100). In particular embodiments, an angular value may be determinedbased at least in part on a position of a component of scanner 120. Asan example, an azimuth or altitude value associated with a pixel 210 maybe determined from an angular position of one or more correspondingscanning mirrors of scanner 120.

FIG. 3 illustrates an example lidar system 100 with an example rotatingpolygon mirror 301. In particular embodiments, a scanner 120 may includea polygon mirror 301 configured to scan output beam 125 along aparticular direction. In the example of FIG. 3, scanner 120 includes twoscanning mirrors: (1) a polygon mirror 301 that rotates along the Θ_(x)direction and (2) a scanning mirror 302 that oscillates back and forthalong the Θ_(y) direction. The output beam 125 from light source 110,which passes alongside mirror 115, is reflected by reflecting surface320 of scan mirror 302 and is then reflected by a reflecting surface(e.g., surface 320A, 320B, 320C, or 320D) of polygon mirror 301.Scattered light from a target 130 returns to the lidar system 100 asinput beam 135. The input beam 135 reflects from polygon mirror 301,scan mirror 302, and mirror 115, which directs input beam 135 throughfocusing lens 330 and to the detector 340 of receiver 140. The detector340 may be a PN photodiode, a PIN photodiode, an APD, a SPAD, or anyother suitable detector. A reflecting surface 320 (which may be referredto as a reflective surface) may include a reflective metallic coating(e.g., gold, silver, or aluminum) or a reflective dielectric coating,and the reflecting surface 320 may have any suitable reflectivity R atan operating wavelength of the light source 110 (e.g., R greater than orequal to 70%, 80%, 90%, 95%, 98%, or 99%).

In particular embodiments, a polygon mirror 301 may be configured torotate along a Θ_(x) or Θ_(y) direction and scan output beam 125 along asubstantially horizontal or vertical direction, respectively. A rotationalong a Θ_(x) direction may refer to a rotational motion of mirror 301that results in output beam 125 scanning along a substantiallyhorizontal direction. Similarly, a rotation along a Θ_(y) direction mayrefer to a rotational motion that results in output beam 125 scanningalong a substantially vertical direction. In FIG. 3, mirror 301 is apolygon mirror that rotates along the Ox direction and scans output beam125 along a substantially horizontal direction, and mirror 302 pivotsalong the Θ_(y) direction and scans output beam 125 along asubstantially vertical direction. In particular embodiments, a polygonmirror 301 may be configured to scan output beam 125 along any suitabledirection. As an example, a polygon mirror 301 may scan output beam 125at any suitable angle with respect to a horizontal or verticaldirection, such as for example, at an angle of approximately 0°, 10°,20°, 30°, 45°, 60°, 70°, 80°, or 90° with respect to a horizontal orvertical direction.

In particular embodiments, a polygon mirror 301 may refer to amulti-sided object having reflective surfaces 320 on two or more of itssides or faces. As an example, a polygon mirror may include any suitablenumber of reflective faces (e.g., 2, 3, 4, 5, 6, 7, 8, or 10 faces),where each face includes a reflective surface 320. A polygon mirror 301may have a cross-sectional shape of any suitable polygon, such as forexample, a triangle (with three reflecting surfaces 320), square (withfour reflecting surfaces 320), pentagon (with five reflecting surfaces320), hexagon (with six reflecting surfaces 320), heptagon (with sevenreflecting surfaces 320), or octagon (with eight reflecting surfaces320). In FIG. 3, the polygon mirror 301 has a substantially squarecross-sectional shape and four reflecting surfaces (320A, 320B, 320C,and 320D). The polygon mirror 301 in FIG. 3 may be referred to as asquare mirror, a cube mirror, or a four-sided polygon mirror. In FIG. 3,the polygon mirror 301 may have a shape similar to a cube, cuboid, orrectangular prism. Additionally, the polygon mirror 301 may have a totalof six sides, where four of the sides include faces with reflectivesurfaces (320A, 320B, 320C, and 320D).

In particular embodiments, a polygon mirror 301 may be continuouslyrotated in a clockwise or counter-clockwise rotation direction about arotation axis of the polygon mirror 301. The rotation axis maycorrespond to a line that is perpendicular to the plane of rotation ofthe polygon mirror 301 and that passes through the center of mass of thepolygon mirror 301. In FIG. 3, the polygon mirror 301 rotates in theplane of the drawing, and the rotation axis of the polygon mirror 301 isperpendicular to the plane of the drawing. An electric motor may beconfigured to rotate a polygon mirror 301 at a substantially fixedfrequency (e.g., a rotational frequency of approximately 1 Hz (or 1revolution per second), 10 Hz, 50 Hz, 100 Hz, 500 Hz, or 1,000 Hz). Asan example, a polygon mirror 301 may be mechanically coupled to anelectric motor (e.g., a synchronous electric motor) which is configuredto spin the polygon mirror 301 at a rotational speed of approximately160 Hz (or, 9600 revolutions per minute (RPM)).

In particular embodiments, output beam 125 may be reflected sequentiallyfrom the reflective surfaces 320A, 320B, 320C, and 320D as the polygonmirror 301 is rotated. This results in the output beam 125 being scannedalong a particular scan axis (e.g., a horizontal or vertical scan axis)to produce a sequence of scan lines, where each scan line corresponds toa reflection of the output beam 125 from one of the reflective surfacesof the polygon mirror 301. In FIG. 3, the output beam 125 reflects offof reflective surface 320A to produce one scan line. Then, as thepolygon mirror 301 rotates, the output beam 125 reflects off ofreflective surfaces 320B, 320C, and 320D to produce a second, third, andfourth respective scan line. In particular embodiments, a lidar system100 may be configured so that the output beam 125 is first reflectedfrom polygon mirror 301 and then from scan mirror 302 (or vice versa).As an example, an output beam 125 from light source 110 may first bedirected to polygon mirror 301, where it is reflected by a reflectivesurface of the polygon mirror 301, and then the output beam 125 may bedirected to scan mirror 302, where it is reflected by reflective surface320 of the scan mirror 302. In the example of FIG. 3, the output beam125 is reflected from the polygon mirror 301 and the scan mirror 302 inthe reverse order. In FIG. 3, the output beam 125 from light source 110is first directed to the scan mirror 302, where it is reflected byreflective surface 320, and then the output beam 125 is directed to thepolygon mirror 301, where it is reflected by reflective surface 320A.

FIG. 4 illustrates an example light-source field of view (FOV_(L)) andreceiver field of view (FOV_(R)) for a lidar system 100. A light source110 of lidar system 100 may emit pulses of light as the FOV_(L) andFOV_(R) are scanned by scanner 120 across a field of regard (FOR). Inparticular embodiments, a light-source field of view may refer to anangular cone illuminated by the light source 110 at a particular instantof time. Similarly, a receiver field of view may refer to an angularcone over which the receiver 140 may receive or detect light at aparticular instant of time, and any light outside the receiver field ofview may not be received or detected. As an example, as the light-sourcefield of view is scanned across a field of regard, a portion of a pulseof light emitted by the light source 110 may be sent downrange fromlidar system 100, and the pulse of light may be sent in the directionthat the FOV_(L) is pointing at the time the pulse is emitted. The pulseof light may scatter off a target 130, and the receiver 140 may receiveand detect a portion of the scattered light that is directed along orcontained within the FOV_(R).

In particular embodiments, scanner 120 may be configured to scan both alight-source field of view and a receiver field of view across a fieldof regard of the lidar system 100. Multiple pulses of light may beemitted and detected as the scanner 120 scans the FOV_(L) and FOV_(R)across the field of regard of the lidar system 100 while tracing out ascan pattern 200. In particular embodiments, the light-source field ofview and the receiver field of view may be scanned synchronously withrespect to one another, so that as the FOV_(L) is scanned across a scanpattern 200, the FOV_(R) follows substantially the same path at the samescanning speed. Additionally, the FOV_(L) and FOV_(R) may maintain thesame relative position to one another as they are scanned across thefield of regard. As an example, the FOV_(L) may be substantiallyoverlapped with or centered inside the FOV_(R) (as illustrated in FIG.4), and this relative positioning between FOV_(L) and FOV_(R) may bemaintained throughout a scan. As another example, the FOV_(R) may lagbehind the FOV_(L) by a particular, fixed amount throughout a scan(e.g., the FOV_(R) may be offset from the FOV_(L) in a directionopposite the scan direction).

In particular embodiments, the FOV_(L) may have an angular size orextent Θ_(L) that is substantially the same as or that corresponds tothe divergence of the output beam 125, and the FOV_(R) may have anangular size or extent Θ_(R) that corresponds to an angle over which thereceiver 140 may receive and detect light. In particular embodiments,the receiver field of view may be any suitable size relative to thelight-source field of view. As an example, the receiver field of viewmay be smaller than, substantially the same size as, or larger than theangular extent of the light-source field of view. In particularembodiments, the light-source field of view may have an angular extentof less than or equal to 50 milliradians, and the receiver field of viewmay have an angular extent of less than or equal to 50 milliradians. TheFOV_(L) may have any suitable angular extent Θ_(L), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Similarly, theFOV_(R) may have any suitable angular extent Θ_(R), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. In particularembodiments, the light-source field of view and the receiver field ofview may have approximately equal angular extents. As an example, Θ_(L)and Θ_(R) may both be approximately equal to 1 mrad, 2 mrad, or 4 mrad.In particular embodiments, the receiver field of view may be larger thanthe light-source field of view, or the light-source field of view may belarger than the receiver field of view. As an example, Θ_(L) may beapproximately equal to 3 mrad, and Θ_(R) may be approximately equal to 4mrad. As another example, Θ_(R) may be approximately L times larger thanΘ_(L), where L is any suitable factor, such as for example, 1.1, 1.2,1.5, 2, 3, 5, or 10.

In particular embodiments, a pixel 210 may represent or may correspondto a light-source field of view or a receiver field of view. As theoutput beam 125 propagates from the light source 110, the diameter ofthe output beam 125 (as well as the size of the corresponding pixel 210)may increase according to the beam divergence Θ_(L). As an example, ifthe output beam 125 has a Θ_(L) of 2 mrad, then at a distance of 100 mfrom the lidar system 100, the output beam 125 may have a size ordiameter of approximately 20 cm, and a corresponding pixel 210 may alsohave a corresponding size or diameter of approximately 20 cm. At adistance of 200 m from the lidar system 100, the output beam 125 and thecorresponding pixel 210 may each have a diameter of approximately 40 cm.

FIG. 5 illustrates an example unidirectional scan pattern 200 thatincludes multiple pixels 210 and multiple scan lines 230. In particularembodiments, scan pattern 200 may include any suitable number of scanlines 230 (e.g., approximately 1, 2, 5, 10, 20, 50, 100, 500, or 1,000scan lines), and each scan line 230 of a scan pattern 200 may includeany suitable number of pixels 210 (e.g., 1, 2, 5, 10, 20, 50, 100, 200,500, 1,000, 2,000, or 5,000 pixels). The scan pattern 200 illustrated inFIG. 5 includes eight scan lines 230, and each scan line 230 includesapproximately 16 pixels 210. In particular embodiments, a scan pattern200 where the scan lines 230 are scanned in two directions (e.g.,alternately scanning from right to left and then from left to right) maybe referred to as a bidirectional scan pattern 200, and a scan pattern200 where the scan lines 230 are scanned in the same direction may bereferred to as a unidirectional scan pattern 200. The scan pattern 200in FIG. 5 may be referred to as a unidirectional scan pattern 200 whereeach scan line 230 travels across the FOR in substantially the samedirection (e.g., approximately from left to right as viewed from thelidar system 100). In particular embodiments, scan lines 230 of aunidirectional scan pattern 200 may be directed across a FOR in anysuitable direction, such as for example, from left to right, from rightto left, from top to bottom, from bottom to top, or at any suitableangle (e.g., at a 0°, 5°, 10°, 30°, or 45° angle) with respect to ahorizontal or vertical axis. In particular embodiments, each scan line230 in a unidirectional scan pattern 200 may be a separate line that isnot directly connected to a previous or subsequent scan line 230.

In particular embodiments, a unidirectional scan pattern 200 may beproduced by a scanner 120 that includes a polygon mirror (e.g., polygonmirror 301 of FIG. 3), where each scan line 230 is associated with aparticular reflective surface 320 of the polygon mirror. As an example,reflective surface 320A of polygon mirror 301 in FIG. 3 may produce scanline 230A in FIG. 5. Similarly, as the polygon mirror 301 rotates,reflective surfaces 320B, 320C, and 320D may successively produce scanlines 230B, 230C, and 230D, respectively. Additionally, for a subsequentrevolution of the polygon mirror 301, the scan lines 230A′, 230B′,230C′, and 230D′ may be successively produced by reflections of theoutput beam 125 from reflective surfaces 320A, 320B, 320C, and 320D,respectively. In particular embodiments, N successive scan lines 230 ofa unidirectional scan pattern 200 may correspond to one full revolutionof a N-sided polygon mirror. As an example, the four scan lines 230A,230B, 230C, and 230D in FIG. 5 may correspond to one full revolution ofthe four-sided polygon mirror 301 in FIG. 3. Additionally, a subsequentrevolution of the polygon mirror 301 may produce the next four scanlines 230A′, 230B′, 230C′, and 230D′ in FIG. 5.

FIG. 6 illustrates an example InGaAs avalanche photodiode (APD) 400.Referring back to FIG. 1, the receiver 140 may include one or more APDs400 configured to receive and detect light from input light such as thebeam 135. More generally, the APD 400 can operate in any suitablereceiver of input light. The APD 400 may be configured to detect aportion of pulses of light which are scattered by a target locateddownrange from the lidar system in which the APD 400 operates. Forexample, the APD 400 may receive a portion of a pulse of light scatteredby the target 130 depicted in FIG. 1, and generate an electrical-currentsignal corresponding to the received pulse of light.

The APD 400 may include doped or undoped layers of any suitablesemiconductor material, such as for example, silicon, germanium, InGaAs,InGaAsP, or indium phosphide (InP). Additionally, the APD 400 mayinclude an upper electrode 402 and a lower electrode 406 for couplingthe ADP 400 to an electrical circuit. The APD 400 for example may beelectrically coupled to a voltage source that supplies a reverse-biasvoltage V to the APD 400. Additionally, the APD 400 may be electricallycoupled to a transimpedance amplifier which receives electrical currentgenerated by the APD 400 and produces an output voltage signal thatcorresponds to the received current. The upper electrode 402 or lowerelectrode 406 may include any suitable electrically conductive material,such as for example a metal (e.g., gold, copper, silver, or aluminum), atransparent conductive oxide (e.g., indium tin oxide), a carbon-nanotubematerial, or polysilicon. In some implementations, the upper electrode402 is partially transparent or has an opening to allow input light 410to pass through to the active region of the APD 400. In FIG. 10, theupper electrode 402 may have a ring shape that at least partiallysurrounds the active region of the APD 400, where the active regionrefers to an area over which the APD 400 may receive and detect theinput light 410. The active region may have any suitable size ordiameter d, such as for example, a diameter of approximately 25 μm, 50μm, 80 μm, 100 μm, 200 μm, 500 μm, 1 mm, 2 mm, or 5 mm.

The APD 400 may include any suitable combination of any suitablesemiconductor layers having any suitable doping (e.g., n-doped, p-doped,or intrinsic undoped material). In the example of FIG. 10, the InGaAsAPD 400 includes a p-doped InP layer 420, an InP avalanche layer 422, anabsorption layer 424 with n-doped InGaAs or InGaAsP, and an n-doped InPsubstrate layer 426. Depending on the implementation, the APD 400 mayinclude separate absorption and avalanche layers, or a single layer mayact as both an absorption and avalanche region. The APD 400 may operateelectrically as a PN diode or a PIN diode, and, during operation, theAPD 400 may be reverse-biased with a positive voltage V applied to thelower electrode 406 with respect to the upper electrode 402. The appliedreverse-bias voltage V may have any suitable value, such as for exampleapproximately 5 V, 10 V, 20 V, 30 V, 50 V, 75 V, 100 V, or 200 V.

In FIG. 6, photons of the input light 410 may be absorbed primarily inthe absorption layer 424, resulting in the generation of electron-holepairs (which may be referred to as photo-generated carriers). Forexample, the absorption layer 424 may be configured to absorb photonscorresponding to the operating wavelength of the lidar system 100 (e.g.,any suitable wavelength between approximately 1400 nm and approximately1600 nm). In the avalanche layer 422, an avalanche-multiplicationprocess occurs where carriers (e.g., electrons or holes) generated inthe absorption layer 424 collide with the semiconductor lattice of theabsorption layer 424, and produce additional carriers through impactionization. This avalanche process can repeat numerous times so that onephoto-generated carrier may result in the generation of multiplecarriers. As an example, a single photon absorbed in the absorptionlayer 424 may lead to the generation of approximately 10, 50, 100, 200,500, 1000, 10,000, or any other suitable number of carriers through anavalanche-multiplication process. The carriers generated in an APD 400may produce an electrical current that is coupled to an electricalcircuit which may perform, for example, signal amplification, sampling,filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection.

The number of carriers generated from a single photo-generated carriermay increase as the applied reverse bias V is increased. If the appliedreverse bias V is increased above a particular value referred to as theAPD breakdown voltage, then a single carrier can trigger aself-sustaining avalanche process (e.g., the output of the APD 400 issaturated regardless of the input light level). The APD 400 that isoperated at or above a breakdown voltage may be referred to as asingle-photon avalanche diode (SPAD) and may be referred to as operatingin a Geiger mode or a photon-counting mode. The APD 400 that is operatedbelow a breakdown voltage may be referred to as a linear APD, and theoutput current generated by the APD 400 may be sent to an amplifiercircuit (e.g., a transimpedance amplifier). The receiver 140 (seeFIG. 1) may include an APD configured to operate as a SPAD and aquenching circuit configured to reduce a reverse-bias voltage applied tothe SPAD when an avalanche event occurs in the SPAD. The APD 400configured to operate as a SPAD may be coupled to an electronicquenching circuit that reduces the applied voltage V below the breakdownvoltage when an avalanche-detection event occurs. Reducing the appliedvoltage may halt the avalanche process, and the applied reverse-biasvoltage may then be re-set to await a subsequent avalanche event.Additionally, the APD 400 may be coupled to a circuit that generates anelectrical output pulse or edge when an avalanche event occurs.

In some implementations, the APD 400 or the APD 400 along withtransimpedance amplifier have a noise-equivalent power (NEP) that isless than or equal to 100 photons, 50 photons, 30 photons, 20 photons,or 10 photons. For example, the APD 400 may be operated as a SPAD andmay have a NEP of less than or equal to 20 photons. As another example,the APD 400 may be coupled to a transimpedance amplifier that producesan output voltage signal with a NEP of less than or equal to 50 photons.The NEP of the APD 400 is a metric that quantifies the sensitivity ofthe APD 400 in terms of a minimum signal (or a minimum number ofphotons) that the APD 400 can detect. The NEP may correspond to anoptical power (or to a number of photons) that results in asignal-to-noise ratio of 1, or the NEP may represent a threshold numberof photons above which an optical signal may be detected. For example,if the APD 400 has a NEP of 20 photons, then the input beam 410 with 20photons may be detected with a signal-to-noise ratio of approximately 1(e.g., the APD 400 may receive 20 photons from the input beam 410 andgenerate an electrical signal representing the input beam 410 that has asignal-to-noise ratio of approximately 1). Similarly, the input beam 410with 100 photons may be detected with a signal-to-noise ratio ofapproximately 5. In some implementations, the lidar system 100 with theAPD 400 (or a combination of the APD 400 and transimpedance amplifier)having a NEP of less than or equal to 100 photons, 50 photons, 30photons, 20 photons, or 10 photons offers improved detection sensitivitywith respect to a conventional lidar system that uses a PN or PINphotodiode. For example, an InGaAs PIN photodiode used in a conventionallidar system may have a NEP of approximately 10⁴ to 10⁵ photons, and thenoise level in a lidar system with an InGaAs PIN photodiode may be 10³to 10⁴ times greater than the noise level in a lidar system 100 with theInGaAs APD detector 400.

Referring back to FIG. 1, an optical filter may be located in front ofthe receiver 140 and configured to transmit light at one or moreoperating wavelengths of the light source 110 and attenuate light atsurrounding wavelengths. For example, an optical filter may be afree-space spectral filter located in front of APD 400 of FIG. 6. Thisspectral filter may transmit light at the operating wavelength of thelight source 110 (e.g., between approximately 1530 nm and 1560 nm) andattenuate light outside that wavelength range. As a more specificexample, light with wavelengths of approximately 400-1530 nm or1560-2000 nm may be attenuated by any suitable amount, such as forexample, by at least 5 dB, 10 dB, 20 dB, 30 dB, or 40 dB.

Next, FIG. 7 illustrates an APD 502 coupled to an examplepulse-detection circuit 504. The APD 502 can be similar to the APD 400discussed above with reference to FIG. 6, or can be any other suitabledetector. The pulse-detection circuit 504 can operate in the lidarsystem of FIG. 1 as part of the receiver 140 or any other suitablereceiver. The pulse-detection circuit 504 alternatively can beimplemented in the controller 150 or another suitable controller. Insome implementations, parts of the pulse-detection circuit 504 canoperate in a receiver and other parts of the pulse-detection circuit 504can operate in a controller. For example, components 510 and 512 may bea part of the receiver 140, and components 514 and 516 may be a part ofthe controller 150.

The pulse-detection circuit 504 may include circuitry that receives asignal from a detector (e.g., an electrical current from the APD 502)and performs current-to-voltage conversion, signal amplification,sampling, filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection, as examples. Thepulse-detection circuit 504 may determine whether an optical pulse hasbeen received by the APD 502 or may determine a time associated withreceipt of an optical pulse by the APD 502. Additionally, thepulse-detection circuit 504 may determine a duration of a receivedoptical pulse. In an example implementation, the pulse-detection circuit504 includes a transimpedance amplifier (TIA) 510, a gain circuit 512, acomparator 514, and a time-to-digital converter (TDC) 516.

The TIA 510 may be configured to receive an electrical-current signalfrom the APD 502 and produce a voltage signal that corresponds to thereceived electrical-current signal. For example, in response to areceived optical pulse, the APD 502 may produce a current pulsecorresponding to the optical pulse. The TIA 510 may receive the currentpulse from the APD 502 and produce a voltage pulse that corresponds tothe received current pulse. The TIA 510 may also act as an electronicfilter. For example, the TIA 510 may be configured as a low-pass filterthat removes or attenuates high-frequency electrical noise byattenuating signals above a particular frequency (e.g., above 1 MHz, 10MHz, 20 MHz, 50 MHz, 100 MHz, 200 MHz, or any other suitable frequency).

The gain circuit 512 may be configured to amplify a voltage signal. Asan example, the gain circuit 512 may include one or morevoltage-amplification stages that amplify a voltage signal received fromthe TIA 510. For example, the gain circuit 512 may receive a voltagepulse from the TIA 510, and the gain circuit 512 may amplify the voltagepulse by any suitable amount, such as for example, by a gain ofapproximately 3 dB, 10 dB, 20 dB, 30 dB, 40 dB, or 50 dB. Additionally,the gain circuit 512 may also act as an electronic filter configured toremove or attenuate electrical noise.

The comparator 514 may be configured to receive a voltage signal fromthe TIA 510 or the gain circuit 512 and produce an electrical-edgesignal (e.g., a rising edge or a falling edge) when the received voltagesignal rises above or falls below a particular threshold voltage VT. Asan example, when a received voltage rises above VT, the comparator 514may produce a rising-edge digital-voltage signal (e.g., a signal thatsteps from approximately 0 V to approximately 2.5 V, 3.3 V, 5 V, or anyother suitable digital-high level). As another example, when a receivedvoltage falls below VT, the comparator 514 may produce a falling-edgedigital-voltage signal (e.g., a signal that steps down fromapproximately 2.5 V, 3.3 V, 5 V, or any other suitable digital-highlevel to approximately 0 V). The voltage signal received by thecomparator 514 may be received from the TIA 510 or the gain circuit 512and may correspond to an electrical-current signal generated by the APD502. For example, the voltage signal received by the comparator 514 mayinclude a voltage pulse that corresponds to an electrical-current pulseproduced by the APD 502 in response to receiving an optical pulse. Thevoltage signal received by the comparator 514 may be an analog signal,and an electrical-edge signal produced by the comparator 514 may be adigital signal.

The time-to-digital converter (TDC) 516 may be configured to receive anelectrical-edge signal from the comparator 514 and determine an intervalof time between emission of a pulse of light by the light source andreceipt of the electrical-edge signal. The output of the TDC 516 may bea numerical value that corresponds to the time interval determined bythe TDC 516. In some implementations, the TDC 516 has an internalcounter or clock with any suitable period, such as for example, 5 ps, 10ps, 15 ps, 20 ps, 30 ps, 50 ps, 100 ps, 0.5 ns, 1 ns, 2 ns, 5 ns, or 10ns. The TDC 516 for example may have an internal counter or clock with a20 ps period, and the TDC 516 may determine that an interval of timebetween emission and receipt of a pulse is equal to 25,000 time periods,which corresponds to a time interval of approximately 0.5 microseconds.Referring back to FIG. 1, the TDC 516 may send the numerical value“25000” to a processor or controller 150 of the lidar system 100, whichmay include a processor configured to determine a distance from thelidar system 100 to the target 130 based at least in part on an intervalof time determined by a TDC 516. The processor may receive a numericalvalue (e.g., “25000”) from the TDC 516 and, based on the received value,the processor may determine the distance from the lidar system 100 to atarget 130.

In one case, a lidar system includes a transmitter with a light sourcethat generates a laser light at an intrinsically eye-safe wavelength,e.g., 1550 nm, and a receiver with a linear-mode avalanche photodiode(APD) detector. Relative to the 905 nm wavelength, where otherautomotive LIDAR systems typically operate, there is an increase in thenumber of photons per mW of energy at the 1550 nm wavelength. Moreover,the 1550 nm wavelength is better suited for complying with eye safetyrequirements. Generally speaking, the system uses a linear-modeavalanche detector (the APD) to better take advantage of the increasednumber of photons returned from the reflected target at the 1550 nmwavelength. Contrary to typical single-photon detectors currently usedin automotive lidar systems (which produce a fixed output upon thedetection of a “single” photon), the linear-mode avalanche detectorproduces an output that is dependent on (e.g., is proportional to) thenumber of photons incident on the detector in a particular time period.The use of this type of detector enables the detection of rising andfalling edge, intensity, and amplitude characteristics of the returnedpulse, which provides for longer range detection and a more robust andaccurate detection system.

As noted above, the use of a linear-mode APD (for example atapproximately the 1550 nm wavelength) provides the opportunity toperform enhanced detection activities on the received reflected lightpulse from a target. It will be noted that, while these systems aredescribed as using a transmitter that transmits light pulses atapproximately the 1550 nm wavelength, the transmitter could transmit atother wavelengths instead (or as well in a multiple wavelength system).For example, the transmitter could transmit pulses at a wavelength belowapproximately 1900 nanometers, at a wavelength between approximately1500 nanometers and 1600 nanometers, at a wavelength above approximately1100 nanometers, above 1400 nanometers, in a range between 1400 and 1900nanometers, in a range between 1530 and 1580 nanometers, etc. In thesecases, the system may use a linear-mode APD formed as aIndium-Gallium-Arsenide (InGaAs) semi-conductor material. Still further,in some instances, the systems described below could use a transmitterthat transmits light pulses having wavelengths below 1100 nanometers,such as between 900 and 1000 nanometers, at approximately 950nanometers, etc. In these cases, the systems may use an APD formed as asilicon semi-conductor material.

Generally, FIG. 8 illustrates a block diagram of a receiver 600configured as a light detector 602, which may be, for example, an APD orother detector 400 illustrated in FIG. 10, disposed directly on anapplication-specific integrated circuit (ASIC) 604. In this case, theASIC 604 is an integrated circuit having circuitry thereon thatprocesses the electrical signals produced by the light detector 602 inresponse to detecting light signals. The light detector 602 may bemounted directly on the ASIC 604 and may have any output that iselectrically connected to an input of the ASIC 604. More particularly,FIG. 8 illustrates a light detector 602 that is directly bump-bonded tothe ASIC 604 which may include or be configured to include a readoutintegrated circuit (ROIC). Generally speaking, an ASIC is any integratedcircuit (IC) customized for a particular use while a ROIC is a specifictype of ASIC designed for reading/processing signals from detectors. Forexample, the light detector 602 may be configured as a CCD array coupledto a ROIC that receives and accumulates charge from each pixel of theCCD. The ROIC may then provide an output signal to a circuit (e.g.,other parts of the ASIC 604) for readout (to determine the amount ofaccumulated charge). The ROIC described here, however, may be differentthan a traditional ROIC, as the ROIC in the system of FIG. 8 may do muchmore than accumulate charge and provide a readout value. Here, the ROICperforms current-to-voltage conversion (with the TIA), voltageamplification, filtering, edge/level detection, timing, and TDC(time-to-digital conversion). As a result, the terms ASIC and ROIC maybe used interchangeably in this description.

Still further, the detector 602 is electrically (and mechanically)connected to the ASIC 604 by “bump bonding” where a small ball of solderis attached to a surface to form a solder “bump.” For example, the bumpsmay be attached to solder pads of the ASIC 604, and the correspondingconnectors of the detector package may then be brought into contact withthe bumps. The two devices are then “bump bonded” (or, soldered)together by heating, to allow the solder bumps to reflow. Bump bondinghas advantages over other types of electrical connectors, includingsmaller overall size (e.g., compared to connecting the ASIC and detectorwith wire or wire bonding), better reliability, higher electrical speed(the shorter distance provided by the bump bond has lower parasiticcapacitance or inductance), and less electrical noise (the signaltravels a relatively short distance from the detector to the ASIC, whichmeans there is less chance for the signal to become degraded orcorrupted by picking up noise).

FIG. 9 illustrates the receiver 600 of FIG. 8 in more detail and, inparticular, depicts an example set of circuitry that may be disposed onthe ASIC 604 of the receiver 600 of FIG. 8. In particular, FIG. 9illustrates the detector 602, which may be any suitable light detectoras described herein, coupled directly to the ASIC 604. The circuitry ofthe ASIC 604 is illustrated in block diagram form in FIG. 9, but it willbe understood that this circuitry may be disposed in any suitable manneron an integrated circuit, such as one that is silicon based. In anyevent, the output of the detector 602 includes one or more electricalsignals produced as a result of the detection of light or photonsarriving in the detector 602, and which are referred to herein as lightdetection signals. These light detection signals are provided to a setof parallel connected amplitude detection circuits 608 on the ASIC 604.Each of the parallel connected amplitude detection circuits 608 isillustrated as including an amplifier 609, a comparator 610 and atime-to-digital converter (TDC) 612. The output of each of the amplitudedetection circuits 608 is provided to an envelope detection circuit 614,which has one or more outputs connected to a range detection circuit616. An amplitude detection circuit 608, which may include a comparator610 and a TDC 612, may be referred to as an amplitude detector, amagnitude detection circuit, or a magnitude detector.

More particularly, the amplifiers 609 amplify the light detectionsignals from the light detector 602 and provide an amplified signal to acomparator 610. While the circuitry of FIG. 9 is illustrated asincluding a separate amplifier 609 disposed in each of the parallelconnected amplitude detection circuits 608, one or more amplifiers(e.g., a TIA 510 and/or a gain circuit 512) could be configured toamplify the light detection signals from the detector 602 prior to thelight detection signals being split and provided to the separateamplitude detection circuits 608. In any event, the output of each ofthe amplifiers 609 is provided to an associated comparator 610 whichcompares the amplified light detection signal to a particular thresholdvalue and outputs a positive or other signal indicating when thecomparison criteria is met. In this case, a separate comparator (labeled610A, 610B, . . . 610N) is illustrated as being disposed in each of theamplitude detection circuits 608. More particularly, each of thecomparators 610 receives an input threshold signal T, indicated morespecifically by a reference number T₁, T₂, . . . T_(n), and compares theamplified light signal to the associated threshold value. Preferably,each of the threshold signals T₁-T_(n) is a different value ranging froma minimum to a maximum value, and these thresholds T will be variousvalues within the expected range of the detected amplitudes of the lightdetection signals produced by the detector 602. Some or all of thethreshold values T may range linearly (e.g., may be equally spacedapart), or may range non-linearly (e.g., be non-equally spaced apart).There may be, for example, more threshold values at the top of theamplitude detection range, at the bottom or lower part of the amplitudedetection range, in the middle of the amplitude detection range, etc.Still further, any number of amplitude detection circuits 608 (andassociated comparators 610 and TDCs 612) may be provided in the ASIC604. Generally speaking, the more amplitude detection circuits that areprovided, the greater or better envelope detection that can be performedby the envelope detector 614.

Still further, as illustrated in FIG. 9, there may be two amplitudedetection circuits 608 associated with each particular threshold value(T₁, for example). In particular, there are two types of comparators610, including rising-edge comparators, indicated with a plus sign (+),and falling-edge comparators, indicated with a minus sign (−). As willbe understood, rising-edge comparators determine when the amplifiedlight detection signal provided at the input thereto reaches or risesabove the threshold T going in a positive or rising direction (that is,reaches the threshold from a lower value). On the other hand,falling-edge comparators determine or detect when the amplified lightdetection signals at the input thereto reach or fall below theassociated threshold T in the negative or falling direction (that is,reach the threshold from a higher value). Thus, the comparator 610A+provides a comparison between the incoming light detection signal to thethreshold T₁, and determines when the incoming light detection signalreaches the level of threshold T₁ going in a positive direction, whilethe comparator 610A− determines when the light signal reaches thethreshold T₁ going in the negative or falling direction. Upon making adetermination that the light detection signal meets the associatedthreshold from the correct direction, the comparator produces an outputsignal that indicates such a condition (i.e., that the comparisoncriteria is met). As illustrated in FIG. 13, the output signal of eachcomparator 610, which may be a direct current (DC) signal, a rising-edgeor falling-edge signal, or a digital bit indicative of the status of thecomparison (e.g., met or not met), is provided to an associated TDC 612.

As explained above, each TDC (including the TDCs 612) includes a veryprecise and high-speed counter or timer, and the TDCs 612 clock, store,and/or output the value or values of the associated timer when the TDC612 receives an appropriate (e.g., positive) input from the associatedcomparator 610. Moreover, each of the TDCs 612 receives a timinginitialization signal t₀, which may generally indicate the time at whichthe lidar system transmitter generated and/or transmitted a light pulseassociated with the current field of regard of the current scan. Thisinitial timing signal to may be provided as an electrical signal from acontroller that controls the transmitter, by a sensor which senses whenthe light pulse is actually transmitted from the transmitter, etc.Moreover, the timing initialization signal to may be generated by thetransmitter based on or to coincide with the rising edge of thetransmitted light pulse, the falling edge of the transmitted lightpulse, the peak or center of the transmitted light pulse or any otherdesired point or location on the transmitted light pulse. Thus, as willbe understood, the TDCs 612 reset and start the counters when theyreceive the to initialization signal, and clock or store the countervalue as a digital output signal when receiving a signal from anassociated comparator 610 that the detected incoming light pulse hasreach a certain threshold T in a rising or falling direction. The TDCs612 may output a digital signal indicating the one or more times thatthe incoming light detection signal met the threshold in the appropriatedirection and these output signals are provided to the envelope detector614.

Of course, all of the TDCs 612 operate in parallel with one anothersimultaneously so that the various amplitude detection circuits 608determine the various different times (relative to the time t₀) at whicha detected light pulse reaches various amplitudes associated with thethresholds T₁-T_(n) in the rising and falling directions.

In some embodiments, an ASIC 604 may include an analog-to-digitalconverter (ADC). As an example, rather than using a parallel arrangementof multiple TDCs, the ASIC 604 may include an ADC configured to producea digital representation of a received pulse. The ADC may be locatedafter the transimpedance amplifier 510 or the gain circuit 512 in FIG. 7and may produce a series of points corresponding to the envelope of areceived pulse (similar to that illustrated in FIG. 10).

As noted above, the envelope detector 614 receives the outputs of theTDCs 612 and analyzes these signals to recreate or produce an indicationof the amplitude of the envelope of the detected light signal over time.An example of such a re-created envelope (which may include pointsindicative of the amplitude or magnitude of the light signal at variouspoints in time) that may be produced by the envelope detector 614 isillustrated in FIG. 10. In the graph of FIG. 10, the received incominglight pulse is re-created based on the signals from the TDCs 612associated with the various thresholds T₁ through T₆. More particularlythe points in the graph of FIG. 10 indicate times (on the x-axis) atwhich one of the amplitude detection circuits 608 of FIG. 9 measuredthat the detected light signal went through one of the amplitudethresholds T₁-T₆ (on the y-axis) in the rising or falling direction. Thetime values t₁ through t₁₁ in FIG. 10 may be referred to as temporalpositions. In the graph of FIG. 10, it will be understood that thedetected light signal passed through the threshold T₁ in a positivedirection at a time t₁ (which is the output of the amplitude detectioncircuit of FIG. 9 having the comparator 610A+), passed through thethreshold T₁ in a negative direction at a time t₁₁ (which is the outputof the amplitude detection circuit having the comparator 610A−), passedthrough the threshold T₂ in a positive direction at a time t₂, (which isthe output of the amplitude detection circuit having the comparator610B+), passed through the threshold T₂ in a negative direction at atime t₁₀ (which is the output of the amplitude detection circuit havingthe comparator 610B−), etc. In this manner, the envelope detector 614may recreate the values of, the amplitude of, or the envelope of thereceived pulse at various times by plotting the threshold valuesassociated with the various amplitude detection circuits 608 in achronological order as determined by the outputs of the TDCs 612 of theamplitude detection circuits 608. In some embodiments, the shape of thepulse received by the APD may not have an identical shape to the pulserecreated by the envelope detector due to variations introduced bysignal processing in the photoreceiver chain.

Once the outputs of the amplitude detection circuits 608 are plotted orordered, the envelope detector 614 may then determine, fill in, orestimate one or more characteristics of the received or detected lightpulse based on these amplitude points to create a complete amplitude ormagnitude envelope associated with the received, scattered light pulseor light signal. For example, the envelope detector 614 may estimate theshape of the received pulse (e.g., the dotted line in FIG. 10) byconnecting the points with a curve fitting routine (which typicallyincludes using three or more points to perform pulse envelopeestimation) or with straight lines, the envelope detector 614 maydetermine the amplitude of the detected light pulse as the highestdetected threshold value or based on a curve fitting routine, theenvelope detector 614 may determine the width of the detected lightpulse in some statistical manner based on the rising and falling edgesof the envelope, the envelope detector 614 may determine the peak orcenter of the detected light pulse based on the rising and falling edgesof the envelope and/or the envelope detector 614 may determine any otherdesired characteristics of the envelope of the detected pulse. In thecase of FIG. 10, the envelope detection circuit 614 may determine thatthe detected light pulse is generally a sinusoidal pulse having amaximum threshold value of T₆.

Of course, the envelope detector 614 may determine other informationregarding the detected pulse, such as the shape, width, peak, center,etc., of the pulse and may provide some or all of this information tothe range detector circuit 616 of FIG. 9. In particular, the rangedetector circuit 616 can use various known or new techniques to detectthe range of the target from which the detected pulse was reflected,based on the round trip time it took the detected pulse to return to thedetector and the speed of light in the appropriate medium (e.g., air).Such a range detector circuit 616 may, for example, use the detectiontime associated with the rising edge, the falling edge, the peak, thecenter, or some other point on the detected pulse. Of course, the rangedetector 616 may use common mathematical techniques to determine therange to the target from the lidar system based on the detected time ofreceipt of the reflected pulse and the speed of light in the appropriatemedium, e.g., air. For example, the range detector circuit 616 may use adetection time associated with a first threshold value crossing on arising edge of a detected pulse and a detection time associated with asecond threshold value crossing on a falling edge of the detected pulseto determine the pulse width of the detected pulse, and use a look-uptable, matrix, or other data structure to determine the time of receiptbased on the pulse width of the detected pulse.

As shown in FIGS. 6-10, the lidar system receives light, such as lightthat has been scattered or reflected by a target, at an avalanchephotodiode (APD) which generates an output current that corresponds tothe intensity of the received light. Although the photodetector in thisembodiment is an APD, other types of photodetectors may be used. The APDoutput is coupled to the transimpedance amplifier (TIA) in thephotoreceiver to convert the output current from the APD to a voltageoutput. The voltage output may then be further amplified or processedand compared against threshold voltage values to create an envelopecorresponding to light received by the APD as shown in FIG. 10.

Each detected envelope may correspond to light emitted by the lidarsystem that has been scattered or reflected by a target back to thelidar system, and the detected envelope may be used to determine, forexample, distance to the target or the amount of energy associated withthe returned light. In particular embodiments, the photoreceiver of thelidar system is designed to work with a wide dynamic range of intensityfrom received light with very low noise. Large currents may be generatedby the APD, for example, by close objects or retroreflectors. Smallcurrents may be generated by distant objects or partially reflectiveobjects. The photoreceiver must be sensitive enough to detectlow-intensity received light that has been scattered or reflected fromdistant objects, as well as robust enough to withstand thehigh-intensity received light that has been scattered or reflected byclose objects without damaging the photoreceiver. For a suitablysensitive TIA that does not have a damage protection mechanism,high-intensity received light can damage the TIA (which may also bereferred to as a pre-amplifier) in the photoreceiver. For example, aresistive short may develop from the gate to drain, gate to source, orboth, in the TIA input stage, which may result in device failure.

If the TIA is designed for high-intensity received light e.g. byincreasing the input capacitance or using protection resistors, then thesignal to noise ratio is reduced. This reduces the system's ability todetect scattered light from distant objects. As described below, inparticular embodiments a protection diode circuit is added to the inputof the TIA. The protection diode circuit allows for a low capacitance onthe input of the TIA to maintain sensitivity sufficient to detectlow-intensity received light while still protecting the TIA fromhigh-intensity received light. As an example, the diode circuit may be aresistor or an active resistor between two diodes to reduce the requiredprotection diode area and minimize capacitance on the input of thepre-amplifier.

The transimpedance amplifier may include a cascode circuit. Inparticular embodiments for a CMOS (Complementary Metal OxideSemiconductor) TIA with cascode, a clamping diode may be added betweenthe common source input node and the intermediate node of the cascode.The clamping diode prevents high currents generated by the APD frominducing an overvoltage event on the gate-to-source and gate-to-drainnodes of the common source stage. This protects circuits that, forexample, use a thin oxide MOSFET (Metal Oxide Semiconductor Field EffectTransistor) for the common source stage of the TIA.

FIG. 11 is a circuit diagram of a portion of the transimpedanceamplifier (TIA), also referred to in variations as a preamplifier, whichin particular embodiments may correspond to the TIA 510 of FIG. 7. Aphotoreceiver of a lidar system has a photodetector 702 that receivesincident light 704, such as light received by the lidar system afterbeing scattered from a target, although the photoreceiver may be used inother types of detection systems. The photodetector output current 706serves as a current input to a TIA 708 that generates an output voltage710 for a gain module and comparator, for example.

In particular embodiments, the TIA portion of the circuit 708 is in theform of a cascode having two stages. The first stage is called the inputstage or common source (CS) stage 714, and the second stage is a cascodeor common gate (CG) stage 712. Both devices 712, 714 of the TIA 708 inthis example are in the form of a thin oxide nFET (n-type Field EffectTransistor) to reduce capacitance in the APD output current 706,although other configurations and characteristics may be preferred. TheCS stage 714 is a transconductance amplifier with a source coupled toground and a drain coupled to the source of the CG stage 712. Thisconnection is at an intermediate low impedance node 716 between the twostages. The drain of the CG stage is the voltage output node 710 of theTIA. The CG stage has a gate coupled to a regulated cascode gate voltagelabeled as Vb₀. The CG stage is coupled between a high impedance node atthe voltage output 710 and a low impedance node 716 between the cascodedevice and the input stage and presents a low capacitance to the inputnode for a larger open loop gain.

A local bias circuit may be used to generate the regulated gate voltageVb₀ to bias the CG stage. The gate voltage Vb₀ is used to keep the twodevices 712, 714 in the correct region of operation.

The gate of CS stage 714 is coupled to a feedback line 718 throughfeedback circuit 720, where in particular embodiments the feedbackcircuit is a resistor. The feedback circuit 720 is coupled on one sideto the current input 706 and on the other side to the voltage outputnode 710.

The TIA is powered by a current source 722 that supplies current from avoltage rail 726 to the drain of the CG stage. This current is designedto provide the desired voltage in the particular circuit implementation.In particular embodiments, a current pinch-off device 724 is coupledbetween the current source and the CG stage to limit the maximum currentsupplied to the preamplifier and to limit the maximum voltage on thevoltage output node 710 and the low impedance node 716. In particularembodiments, this device may be a thick oxide nFET connected so that thedrain is coupled to the current source and the source is coupled to thedrain of the CG stage at the high impedance node 710. In such aconfiguration, the gate controls the current pinch-off based on the gatebias voltage Vb₁.

The TIA and the downstream components, e.g. the amplifier, comparator,and TDC, have a maximum input voltage that in some embodiments istypically between 1 V and 2 V. The gate bias voltage Vb₁ can beconfigured to track changes in the threshold voltages of the amplifierdevices 712, 714, and 724 in order to keep the voltage below the maximuminput voltage. In this way, the current pinch-off device protects thetransimpedance amplifier and downstream components from overvoltageconditions.

An input protection diode 728 may be coupled to the output of thephotodetector to protect the TIA from high currents. The diode cathodeis coupled to the output node of the APD 702 at one end. The diode anodeis grounded. Although the diode is connected directly to ground in theillustrated embodiments, in other embodiments the diode anode may becoupled indirectly to a ground through one or more additionalcomponents. The diode 728 serves as input protection for the TIA andsinks current from the APD to ground when the output current from thephotodetector is high, which causes the voltage at the cathode of thediode to exceed the diode barrier voltage. The diode provides a currentaway from the TIA input to protect the sensitive TIA input stage 714.The diode is configured to have a barrier voltage that is selected to bebelow a damage threshold of the TIA, and in some embodiments, below adamage threshold of the CS stage 914. The output current generated bythe APD may be high for a variety of reasons, but a high current maycommonly occur when the output laser strikes a nearby highly-reflectiveobject, but can be caused by other particularly reflective orilluminated objects or by other light sources in the field of view.Sinking these occasional high currents allows the amplifier to be mademore sensitive while still protecting the amplifier from damage.

The amplifier is further protected by a clamping diode 730 with acathode coupled to the low impedance intermediate node of the amplifierand an anode coupled to the gate node of the CS stage 714. Under smallsignals the diode is reverse biased. With large signals the diodebarrier voltage is exceeded and the forward current is turned on. Theforward current helps keep the delta voltage between the gate and theintermediate node, as well as between the gate and ground, within a safevoltage range. The selected overvoltage depends on the characteristicsof the diode and is typically below the maximum input voltage of between1 V and 2 V. The clamping diode will allow a forward current flow toprevent an overvoltage above the selected maximum input voltage betweenthe gate node and the intermediate node. The clamping diode 730 protectsthis amplifier in particular and may also protect other coupled devices.

FIG. 12 is an alternative circuit diagram of a portion of a TIA suitablefor use in the applications described above. In particular embodiments,an APD 802 generates current when struck by incident light 804, such aslaser emissions retro-reflected by an object in front of the laseremitter. The magnitude of the output current from the APD varies withthe intensity of the incident light. The output current from the APD isinput to a transimpedance amplifier (TIA) 808. The TIA has a cascodewith two stages. The first stage is called the input stage or commonsource (CS) stage 814, and the second stage is a cascode or common gate(CG) stage 812. The CS stage 814 is between the intermediate node andground. The voltage output node 810 is coupled through a feedback line818 from the drain of the CG stage 812 through the feedback and testcircuit logic 820 to both the input node 806 and the gate of the CSstage 814. As in the other examples, the TIA generates an output voltage810 that tracks the input current 806. The feedback and test logicallows for many additional test, maintenance, and calibration functionsto be provided.

The current source in particular embodiments is in the form of a thickoxide pFET switch 822 coupled between a higher voltage rail 826 and thedrain of the CG stage 812 of the TIA. The switch is regulated by acontrolled voltage Vb₂ which is higher than the current pinch off biasVb₁.

In addition, a current pinch-off circuit implemented as a regulated nFET824 between the current source 822 and the drain of the CG stage 812pinches off excess currents from the current source 822 by shutting offcurrent when the voltage on the TIA output 810 is too high. Thisovervoltage protection device operates similarly to the currentpinch-off FET described in the context of FIG. 11.

In particular embodiments, an input protection diode circuit 840 is inthe form of two parallel diodes 842, 844, each with grounded anodes andwith cathodes coupled to the readout circuit output node 806 whichcorresponds to the photo-detector 802 cathode. The two parallelprotection diodes may be similar in size to full ESD (Electro-StaticDischarge) protection diodes. These diodes help sink current from theAPD cathode under large signal conditions.

The cathodes of the two diodes, 842, 844 are connected across anisolating current limit resistor 846. The resistor causes a smallvoltage difference between the two diode cathodes. As a result, thecurrent first sinks through the diode 842 closest to the APD 802 andbefore the resistor 846. The isolating resistor 846 also helps toprevent large currents from flowing toward the sensitive inputtransistor 814 of the TIA. As the voltage on the APD output rises, thefirst diode 842 will provide a current path to ground before the seconddiode 844. As the voltage on the APD output continues to rise, thebarrier voltage at the second diode 844 will also be exceeded causing asecond current path to ground to further ensure protection of the TIAinput path. The resistor (or active resistor) between the two diodesalso reduces the required protection diode area and minimizescapacitance on the input of the pre-amplifier. In particularembodiments, the second diode 844 may be configured with the samebarrier voltage as the first diode 842. In other embodiments, the seconddiode may be configured with a higher barrier voltage than the firstdiode. This complements the effect of the isolating resistor in causingthe first diode to absorb most of the overvoltages.

The amplifier is further protected by a clamping diode 830. Inparticular embodiments, the clamping diode is implemented as adiode-connected nFET, coupled between the low impedance intermediatenode 816 of the amplifier and the input node of the CS stage 814. Thediode connected FET has the drain and gate coupled to the intermediatenode and the source coupled gate of the CS stage 714. The clamping diodewill allow a current flow to prevent an overvoltage above the selectedmaximum input voltage between the input node of the CS stage 814 and theintermediate node 816. The clamping diode 830 regulates the intermediatenode 816 of the TIA by shunting over voltages back to the input node ofthe input stage 714.

FIG. 13 is another alternative circuit diagram of a TIA with protectioncircuits. As in the prior examples, the TIA 908 is in the form of acascode with an input or CS stage 914 and a cascode or CG stage 912. APD902 generates output current 906 when struck by incident light 904, suchas laser emissions retro-reflected by an object in front of the laseremitter. The magnitude of the output current 906 from the APD varieswith the intensity of the incident light. The output current 906 isdirected to the input device 914. The drain from the input stage 914 iscoupled to the source of the cascode stage 912 at an intermediate node916. The cascode stage generates a voltage output at its drain 910 thattracks the input current 906. A feedback line 918 from the voltageoutput node 910 is coupled to a feedback circuit 920 which may be assimple as a resistor. The TIA 908 is fed by a current source 922 coupledto a supply voltage 926.

The TIA 908 is protected from the current source 922 by a currentpinch-off circuit 924 as described above. The TIA is also protected by adiode input circuit 940. The TIA is also protected by clamp diodes 930,934.

A clamping diode 930 is coupled between the intermediate node 916 of thecascode chain and the input stage 914 input gate as discussed above. Asecond parallel diode 934 in the reverse direction with the anodecoupled to the intermediate node and the cathode coupled to the inputgate of the input stage 914 helps to protect against current in theopposite direction. As shown, the two clamp diodes 930, 934 areconnected in parallel but in opposite directions. While these are shownas simple diodes, as an example, one or both may be implemented asdiode-connected FETs as in FIG. 12 or as another type of MOS diode.

Three different protection circuits are described herein and in severalvariations, a clamping diode 830, a current pinch-off switch 824 and aprotection diode circuit 840. While these are shown in combination inFIGS. 11 and 12. Each one may be used without the others or with onlyone of the others. Accordingly, the clamping diode may be sufficient toprotect the TIA and used without the current pinch-off switch or theprotection diode circuit. Similarly, the protection diode circuit may besufficient to protect the TIA and used without the clamping diode or thecurrent pinch-off switch. Similarly, the current pinch-off switch may besufficient to protect the TIA and used without the protection diodecircuit or the clamping diode.

The described receiver and associated circuitry may take any suitablephysical form, including part of an embedded computer system, asystem-on-chip (SOC), a single-board computer system (SBC), or anysuitable combination of two or more of these. As another example, all orpart of the receiver may be combined with, coupled to, or integratedinto a variety of devices, including, but not limited to, a camera,vehicle display (e.g., odometer display or dashboard display), vehiclenavigation system, lidar system, ADAS, autonomous vehicle,autonomous-vehicle driving system, cockpit control, camera view display(e.g., display of a rear-view camera in a vehicle), eyewear, orhead-mounted display. Where appropriate, the receiver may be part of oneor more computer systems that are unitary or distributed; span multiplelocations; span multiple machines. Where appropriate, the receiver mayperform without substantial spatial or temporal limitation one or moreoperations described or illustrated herein. As an example operations maybe performed in real time or in batch mode one or more steps.

In particular embodiments, all or part of a module, circuit, system,method, or algorithm disclosed herein may be implemented or performed bya general-purpose single- or multi-chip processor, a digital signalprocessor (DSP), an ASIC, a FPGA, any other suitable programmable-logicdevice, discrete gate or transistor logic, discrete hardware components,or any suitable combination thereof. A general-purpose processor may bea microprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

In particular embodiments, certain features described herein in thecontext of separate implementations may also be combined and implementedin a single implementation. Conversely, various features that aredescribed in the context of a single implementation may also beimplemented in multiple implementations separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination may in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

While operations may be depicted in the drawings as occurring in aparticular order, this should not be understood as requiring that suchoperations be performed in the particular order shown or in sequentialorder, or that all operations be performed. Further, the drawings mayschematically depict one more example processes or methods in the formof a flow diagram or a sequence diagram. However, other operations thatare not depicted may be incorporated in the example processes or methodsthat are schematically illustrated. For example, one or more additionaloperations may be performed before, after, simultaneously with, orbetween any of the illustrated operations. Moreover, one or moreoperations depicted in a diagram may be repeated, where appropriate.Additionally, operations depicted in a diagram may be performed in anysuitable order. Furthermore, although particular components, devices, orsystems are described herein as carrying out particular operations, anysuitable combination of any suitable components, devices, or systems maybe used to carry out any suitable operation or combination ofoperations. In certain circumstances, multitasking or parallelprocessing operations may be performed. Moreover, the separation ofvarious system components in the implementations described herein shouldnot be understood as requiring such separation in all implementations,and it should be understood that the described program components andsystems may be integrated together in a single software product orpackaged into multiple software products.

Various embodiments have been described in connection with theaccompanying drawings. However, it should be understood that the figuresmay not necessarily be drawn to scale. As an example, distances orangles depicted in the figures are illustrative and may not necessarilybear an exact relationship to actual dimensions or layout of the devicesillustrated.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes or illustrates respective embodimentsherein as including particular components, elements, functions,operations, or steps, any of these embodiments may include anycombination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination, unless expressly indicated otherwiseor indicated otherwise by context. Therefore, herein, the expression “Aor B” means “A, B, or both A and B.” As another example, herein, “A, Bor C” means at least one of the following: A; B; C; A and B; A and C; Band C; A, B and C. An exception to this definition will occur if acombination of elements, devices, steps, or operations is in some wayinherently mutually exclusive.

As used herein, words of approximation such as, without limitation,“approximately, “substantially,” or “about” refer to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skill in the art recognize themodified feature as having the required characteristics or capabilitiesof the unmodified feature. In general, but subject to the precedingdiscussion, a numerical value herein that is modified by a word ofapproximation such as “approximately” may vary from the stated value by±0.5%, ±1%, ±2%, ±3%, ±4%, ±5%, ±10%, ±12%, or ±15%.

As used herein, the terms “first,” “second,” “third,” etc. may be usedas labels for nouns that they precede, and these terms may notnecessarily imply a particular ordering (e.g., a particular spatial,temporal, or logical ordering). As an example, a system may be describedas determining a “first result” and a “second result,” and the terms“first” and “second” may not necessarily imply that the first result isdetermined before the second result.

As used herein, the terms “based on” and “based at least in part on” maybe used to describe or present one or more factors that affect adetermination, and these terms may not exclude additional factors thatmay affect a determination. A determination may be based solely on thosefactors which are presented or may be based at least in part on thosefactors. The phrase “determine A based on B” indicates that B is afactor that affects the determination of A. In some instances, otherfactors may also contribute to the determination of A. In otherinstances, A may be determined based solely on B.

As used herein, the terms “coupled,” “couple,” “coupling” and similarterms may be used to describe or present a direct physical connectionwithout any intermediate components or may refer to a connection that isthrough other intermediate components including resistors, capacitor,diodes, transistors, and integrated circuits. A component may also be“coupled” to another component through modulators, converters, andcommunications interfaces.

1. A transimpedance amplifier protection circuit comprising: a photoreceiver for a lidar system having a photodetector configured to generate an output current in response to received light; a transimpedance amplifier configured to receive the output current and generate a voltage output corresponding to the output current in response thereto; and a diode circuit having a cathode coupled at a node between the photodetector output and the transimpedance amplifier input.
 2. The circuit of claim 1, wherein the diode circuit has a grounded anode.
 3. The circuit of claim 1, wherein the diode circuit is configured to reduce the capacitance at the transimpedance amplifier input.
 4. The circuit of claim 1, wherein the diode circuit has a barrier voltage above which the diode circuit provides a current path to ground, wherein the barrier voltage is below the damage threshold of the transimpedance amplifier.
 5. The circuit of claim 1, wherein the diode circuit comprises a first and a second parallel diode, each with grounded anodes and each with cathodes coupled to the node and a resistor between the two cathodes.
 6. The circuit of claim 4, wherein the resistor is an active resistor.
 7. The circuit of claim 4, wherein the first diode cathode is between the photodetector and the resistor and wherein the second diode has a higher barrier voltage than the first diode.
 8. The circuit of claim 4, wherein the first diode cathode is between the photodetector and the resistor and wherein the first diode and second diode have equivalent barrier voltages.
 9. The circuit of claim 4, wherein the resistor is configured as a current limiting resistor to reduce high currents from the photodetector to the transimpedance amplifier.
 10. An active camera system, comprising: a light source configured to emit light as a series of one or more light pulses; a scanner configured to direct the one or more light pulses towards a remote target at a particular position in a two-dimensional field of regard; and a receiver configured to detect one or more light pulses scattered by the remote target, the receiver including: a photoreceiver having a photodetector configured to generate an output current in response to received light; a transimpedance amplifier configured to receive the output current and generate a voltage output corresponding to the output current in response thereto; and a diode circuit having a cathode coupled at a node between the photodetector output and the transimpedance amplifier input.
 11. A method of imaging a remote target, comprising: generating a light pulse for a position in a two-dimensional scanning field of regard; emitting the generated light pulse toward a remote target in the position of the two-dimensional field of regard; receiving a scattered light pulse scattered from the remote target at a photodetector and generating a current output; generating a voltage output corresponding to the current output at a transimpedance amplifier configured to receive the photodetector output; sinking current from the photodetector to ground when the current output exceeds a barrier voltage of a diode circuit having a grounded anode and a cathode coupled at a node between the photodetector output and the transimpedance amplifier input; detecting a receive time associated with the received scattered light pulse; determining a range to the target based on the receive time of the received scattered light pulse; detecting an intensity of the received scattered light pulse; and determining a reflectivity of the remote target from the determined range to the remote target and the detected intensity of the received scattered light pulse.
 12. A protection circuit for a transimpedance amplifier comprising: an input node of the amplifier coupled to a photodetector, the photodetector configured to generate an output current in response to received light; an intermediate node of the transimpedance amplifier; and a clamping diode coupled between the input node and the intermediate node and configured to prevent overvoltage between the input node and the intermediate node.
 13. The circuit of claim 12, wherein the transimpedance amplifier comprises a common source stage and a common gate stage and wherein the intermediate node is between the common source stage and the common gate stage.
 14. The circuit of claim 13, wherein the clamping diode is configured to prevent the overvoltage between a gate and a drain of the common source stage.
 15. The circuit of claim 13, wherein the clamping diode is configured to prevent the overvoltage between a gate and a source of the common source stage.
 16. The circuit of claim 12, wherein the clamping diode comprises a diode connected field effect transistor.
 17. The circuit of claim 12, wherein the clamping diode has an anode coupled to the input node and a cathode coupled to the intermediate node.
 18. The circuit of claim 17, wherein the clamping diode further comprises a second parallel diode having an anode coupled to the intermediate node and a cathode coupled to the input node.
 19. The circuit of claim 12, further comprising: a current source coupled to a voltage output node of the transimpedance amplifier; and a current pinch off circuit between the current source and the output node configured to pinch off the current when the output voltage exceeds a second overvoltage.
 20. The circuit of claim 19, wherein the current pinch off circuit is a field effect transistor, having a regulated input bias voltage.
 21. The circuit of claim 20, wherein the regulated input bias voltage is regulated based, at least in part, on threshold voltages of the transimpedance amplifier.
 22. The circuit of claim 19, wherein the transimpedance amplifier comprises a cascode chain and wherein the current pinch-off circuit is coupled between the current source and the cascode chain. 